بخش 02

The girls and boys started over toward the mill for a closer inspection. At that same moment the guard came to the door. “Just as I told you,” he called out to Chet. “No openings! Sorry!”

“Too bad, Chet,” Joe said sympathetically. “Well, at least you can keep on relaxing.”

Despite his disappointment, Chet grinned. “Right now I’m starved. “Let’s go down to the river and have our picnic.”

He thanked the guard, and the young people started to walk away. Suddenly Frank stopped and looked back at the mill. Propped against the south wall was a bicycle. Quickly he ran over to examine it. “This looks like a Belgian model,” Frank thought. “Sure is,” he told himself. “The same type Ken Blake has.”

On impulse Frank pulled the pedal from his pocket and compared it to those on the bike. They matched exactly. Frank noticed that one of the pedals looked much less worn than the other. “As if it had been replaced recently,” he reflected, wondering excitedly if someone had used this bicycle to deliver the warning note.

“And could this bike be Ken’s?” the young detective asked himself.He inspected the front-wheel spokes. None was twisted, but several had slight dents. “They could’ve been straightened out easily,” Frank reasoned, “and the paint scratches on the fender touched up.”

He felt his heart beat faster as he waved his companions to join him. When Frank pointed out the clues to his brother, Joe agreed immediately.

“It could be the bicycle which was used to deliver the message-“

Joe was interrupted by a strange voice behind them. “Pardon me, but why are you so interested in that bike?”

Frank quickly slipped the pedal into his pocket as the group swung around to face the speaker. He was the man who had been clipping the hedges.

“Because just yesterday we met a boy, Ken Blake, who was riding a bike of the same model. We don’t often see this Belgian make around.”

For a moment the man looked surprised, then smiled. “Of course! Ken works here-does odd jobs for us around the mill. You must be the boys he met yesterday when he was delivering some copy to the printer.”

“Yes,” Frank replied. “When we asked Ken about his job he was very secretive.”

“Well,” the maintenance man said, “he has to be! This plant is doing top-secret work. All of us have been impressed with the necessity of not talking about Elekton at all.”

“Is Ken around?” Joe asked nonchalantly. “We’d like to say hello.”

“I’m afraid not,” was the reply. “We sent him by bus this afternoon to do an errand. He won’t be back until later.” The man excused himself and resumed his clipping.

“We’d better eat.” Iola giggled. “My poor brother is suffering.”

“I sure am!” Chet rolled his eyes. Laughing, the picnickers started away.

Joe, who was in the rear, happened to glance up at the front of the mill. He was startled to catch a glimpse of a face at one of the second-story windows. He stopped in his tracks.

“Ken Blake I” Joe said to himself.

As the young sleuth stared, mystified, the face disappeared from the window.

CHAPTER VI

A Mysterious Tunnel

PUZZLED, Joe continued looking up at the window of the old mill.

“What’s the matter?” Iola asked him. “Did you see a ghost?”In a low whisper Joe explained about the face which had disappeared. “I’m sure it was Ken Blake I saw at that window!”

The others followed his gaze. “No one’s there now,” Iola said. “Of course the glass in all the windows is old and wavy. The sunlight on them could cause an illusion.”

Chet agreed. “How could Ken be here if he was sent on an errand?”

Joe stood for a minute, deep in thought. “I can’t figure it out, but I’m sure that it was no illusion. Come on, Frank. Let’s go check.”

While the others walked down the hill, the Hardys strode up to the maintenance man, who was still trimming hedges.

“Are you sure Ken went into town?” Joe asked. “Just now I thought I saw him looking out a second-floor window.”

“You couldn’t have. You must have been dreaming.” The man gave a jovial laugh.

Joe was still not convinced. Impulsively he asked, “Does Ken ever run any errands for you at night?”

“No,” the man answered readily. “He leaves his bike here and walks home when we close at five-thirty.”

“Does anyone else have access to the bike after that?” Frank queried.

“It’s kept in an open storage area under the rear of the mill and could be taken from there easily.”

Although obviously curious, the man did not ask the Hardys the reason for their questions. He looked at his watch.

“Excuse me, boys, I’m late for lunch.” He turned and hurried into the mill.

As the brothers hastened to catch up with Chet and the girls, Frank said, “Another thing which makes me wonder if that bicycle is connected with the warning is the description of the boy who bought the pedal.

He could be Ken Blake.”

“I agree,” Joe said. “I’d sure like to question Ken.”

“We’ll come back another time,” Frank proposed.

The group picked up the picnic hamper from the Queen and strolled down a narrow path, through the woods leading to Willow River.

“Here’s a good spot.” Callie pointed to a shaded level area along the bank. “We haven’t been in this section before.”

Soon everyone was enjoying the delicious lunch the girls had prepared: chicken sandwiches, potato salad, chocolate cake, and lemonade. While they were eating, the girls were the targets of good-natured kidding.

“Boy!” Joe exclaimed as he finished his piece of cake. “This is almost as good as my mother and Aunt Gertrude make.”

“That’s a compliment!” Chet said emphatically.Callie’s eyes twinkled. “I know it is. Joe’s mother and aunt are the best cooks ever!”

Iola sniffed. “I don’t know about this compliment stuff. There’s something on your mind, Joe Hardy!”

Joe grinned. “How are you on apple pie and cream puffs and-?”

“Oh, stop it!” Iola commanded. “Otherwise, you won’t get a second piece of cake!”

“I give up.” Joe handed over his paper plate.

After lunch everyone but Chet was ready to relax in the sun. Normally he was the first one to suggest a period of rest, even a nap, but now his new project was uppermost in his mind.

“Let’s start to collect the specimens for my microscope,” he urged his friends.

The Hardys groaned good-naturedly at Chet’s enthusiasm, but readily agreed.

“We’ll need some exercise to work off that meal.” Frank grinned.

The girls packed the food wrappings in the hamper. Then, single file, the group walked downstream, paying careful attention to the rocks and vegetation. Chet picked up several rocks and leaves, but discarded them as being too common.

“Are you looking for something from the Stone Age?” Joe quipped. “Maybe a prehistoric fossil?”

“Wouldn’t you be surprised if I found one?” Chet retorted.

They followed a bend in the river and came to a small cove with a rocky, shelving beach. Here the willow trees did not grow so thickly. The shoreline curved gently around to the right before it came to a halt in a sandy strip along the riverbank.

“What a nice spot,” said Callie. “We’ll have to come here again and wear our swim suits.”

“Look!” cried Iola. “What’s that?”

She pointed to a dark opening beneath a rocky ledge which bordered the beach.

“A cave!” exclaimed Joe and Frank together.

Intrigued, the five hurried along the beach for a closer look. Eagerly the Hardys and Chet peered inside the entrance. The interior was damp, and the cave’s walls were covered with green growth.

“This’ll be a perfect spot to look for specimens,” Chet said. “Let’s go in!”

The boys entered the cave. The girls, however, decided to stay outside.

“Too spooky-and crowded!” Callie declared. “Iola and I will sun ourselves while you boys explore.”

The Hardys and Chet could just about stand up in the low-ceilinged cave. Frank turned on his pocket flashlight and pointed to an unusual yellow-green fungus on the right side of the cave. “Here’s a good sample of lichens, Chet.”

Soon the boys were busy scraping various lichens off the rocks. Gradually they moved deeper into the cave. Frank halted in front of a pile of rocks at the rear.

“There ought to be some interesting specimens behind these stones,” he said. “They look loose enough tomove.”

Together, the three boys rolled some of the rocks to one side. To their great surprise, the stones had concealed another dark hole.

“Hey! This looks like a tunnel!”

Excitedly Joe poked his flashlight into the opening. In its beam they could see that the hole appeared to extend into the side of the bank.

“Let’s see where the tunnel goes!” Joe urged.

“Okay,” Frank agreed eagerly. “We’ll have to move more of these rocks before we can climb through. I wonder who put them here and why.”

Rapidly the boys pushed rocks aside until the narrow tunnel entrance was completely exposed. Joe crawled in first, then Frank.

Chet tried to squeeze his bulky form through the space but quickly backed out. “It’s too tight for me,” he groaned. “I’ll stay here and collect more specimens. Anyhow, I’ll bet some animal made the tunnel and it doesn’t lead anywhere.”

“I’m sure no animal did this,” Joe called back, aiming his flashlight at the earthen walls of the tunnel. “Look how hard-packed the sides are-as if dug out by a shovel,”

Frank was of the same opinion. He pointed to rough-hewn wooden stakes placed at intervals along the sides and across the ceiling. “I wonder who put those supports here-and when.”

The Hardys crawled ahead carefully. There was just room in the passageway for a normal-sized person to get through.

Presently Joe called back to his brother, “Look ahead! I can see a sharp bend to the right. Let’s keep going.”

Frank was about to reply when the brothers were startled by a girl’s scream from outside.

“That’s Callie!” Frank exclaimed. “Something’s wrong!”

CHAPTER VII

Sleuthing by Microscope

FRANK and Joe scrambled through the tunnel and out of the cave. They found Chet and the girls staring at an arrow embedded in the sandy beach.

“It-it almost hit us,” Iola quavered. Callie, who was white-faced with fear, nodded.

Joe was furious. “Whoever shot it shouldn’t be allowed to use such a dangerous weapon!” he burst out.

“That’s a hunting arrow-it could have caused serious injury.”Chet gulped. “M-maybe the Indians haven’t left here, after all,” he said, trying to hide his nervousness.

Joe turned to dash off into the woods to search for the bowman.

“Wait!” Frank called. He had pulled the arrow from the sand. “This was done deliberately,” he announced grimly, holding the arrow up for all of them to see. Attached to the shaft just below the feathers was a tiny piece of paper. It had been fastened on with adhesive tape.

Frank unrolled the paper and read the printed message aloud: “ ‘Danger. Hardys beware.’ “ Chet and the girls shuddered and looked around fearfully, as though they expected to see the bowman behind them. “You boys are involved in a new mystery!” Callie exclaimed. “Your own or your father’s?”

Frank and Joe exchanged glances. It certainly seemed as though they were involved, but they had no way of knowing which case. Did it involve the counterfeit money? Or was it the case their father could not divulge?

“A warning did come to Dad,” Frank admitted. “This one obviously was meant for Joe and me. Whoever shot the arrow trailed us here.”

Joe frowned. “I wonder if the same person sent both warnings.”

“I still think Ken Blake could give us a clue,” Frank said. “But we must remember that anybody could have taken the bike from the storage place under the mill.”

Frank pocketed the latest warning, then the five searched quickly for any lead to the bowman. They found none. When the group returned to the beach, Joe looked at the sky. “We’re in for a storm-and not one of us has a raincoat.” The bright summer sun had disappeared behind towering banks of cumulus clouds. There were rumbles of heavy thunder, followed by vivid flashes of lightning. The air had become humid and oppressive.

“Let’s get out of here!” Chet urged. “This isn’t a picnic any more!”

The young people hastened through the woods and up the road to Chet’s jalopy. As they drove off, rain began coming down in torrents. The sky grew blacker.

Callie shivered. “It seems so sinister-after that awful arrow.”

Chet dropped his sister off at the Morton farm and at the same time picked up his new microscope. He begged to try out the instrument on both warning notes and the Hardys smilingly agreed, although they had an up-to-date model of their own.

By the time they had said good-by to Callie at her house, and Chet had driven the Queen into the Hardys’ driveway, the storm had ended. The sun shone brightly again.

Immediately the three boys went to the laboratory over the garage. Here Frank carefully dusted the arrow and the second warning note for prints. He blew the powder away, and Joe and Chet looked over his shoulder as he peered through the magnifying glass.

“Nothing. Same as the warning to Dad. The person no doubt wore gloves.”

“Now to compare this paper to the first note,” Joe said.

“Right,” his brother agreed, “You have the combination to the cabinet in Dad’s study. Chet and I will rig up his microscope while you get the note from the file.”Frank and Chet focused and adjusted the microscope, making sure it was level on the table. They plugged in the illuminator and checked to see that it did not provide too dazzling a reflection. When Joe returned, Chet took the two pieces of paper and fitted them side by side under the clips on the base.

“Okay. Want to take a look, fellows?”

Frank, then Joe, studied both papers. “The quality and texture are definitely the same,” Frank observed.

Next, he lifted the second note from under the clips and slowly moved the paper back and forth under the lenses.

“A watermark!” he exclaimed, stepping back so the others could look at the small, faint imprint.

“Sure is!” said Joe. “A five-pointed star. This could be a valuable clue! We can try to track down exactly where this paper came from.”

“And also the arrow,” said Chet. “I’ll make the rounds of sport stores in town.”

“Swell, Chet. Thanks,” Frank said.

After their friend had left, the Hardys consulted the classified directory for paper manufacturers.

They made several calls without any luck. Finally they learned that the Quality Paper Company in Bridgeport manufactured paper bearing the five-pointed star watermark. The brothers wanted to go at once to get more information, but realized this errand would have to wait.

“Dad will be home soon,” Frank reminded his brother. “We don’t want to miss our surprise!”

“Right, And I’d like to tell him about the warning on the arrow.”

When Chet returned from a round of the sports shops, he was glum. “I wasn’t much help,” he said. “The arrow isn’t new, and all the stores I checked told me it was a standard model that could be purchased at any sports shop in the country.”

“Never mind, Chet,” said Frank. “At least giving your microscope a trial run helped us to spot the watermark on the second warning note. We’ve located a company that manufactures paper with the star watermark.”

Chet’s face brightened. “Let me know if you find out anything else,” he said, packing up his microscope.

“I guess I’ll take off-and do some nature study for a change.”

After he had driven off, Frank and Joe walked to the house. Their minds once more turned to the surprise Mr. Hardy had for them.

“Wouldn’t it be terrific if-“ Joe said to Frank excitedly. “Do you think it is?”

“I’m just hoping.” Frank grinned.

Just then a newsboy delivered the evening newspaper. The brothers entered the house and went into the living room. Frank scanned the front page and pointed out an item about new trouble in an Indiana electronics plant.

“That’s where an explosion took place a couple of months ago,” Joe remarked. “Sabotage, the investigators decided.”“And before that,” Frank added, “the same thing happened at a rocket research lab in California. Another unsolved case.”

“Seems almost like a chain reaction,” Frank remarked.

Any mystery appealed to the boys, but they did not have much chance to discuss this one. The telephone rang. Aunt Gertrude, after taking the call, burst into the living room. From the look on her face Frank and Joe could tell she was indignant, and at the same time, frightened.

“What’s the matter, Aunty?” Joe asked.

“More threats-that’s all!” she cried out. “This time by telephone. A man’s voice-he sounded sinister-horrible!”

Mrs. Hardy came into the living room at that moment. “What did he say, Gertrude?” she asked.

Aunt Gertrude took a deep breath in an effort to calm down. “ ‘Hardy and his sons are playing with fire,”

the man said. ‘They’ll get burned if they don’t lay off this case.’” Miss Hardy sniffed. “I don’t know what case he meant. What kind of danger are you boys mixed up in now?”

Frank and Joe smiled wryly. “Aunt Gertrude,” Frank replied, “we really don’t know. But please try not to worry,” he begged her and his mother. “You know that Dad and the two of us will be careful.”

When Mr. Hardy came home a little later, his family told him about the threatening telephone call. The boys, however, did not mention the arrow warning in the presence of their mother and Aunt Gertrude.

They knew it would only add to their concern.

Mr. Hardy was as puzzled as his sons. “It’s a funny thing,” he said. “At this point it’s impossible to tell which ‘case’ the person is referring to. If I knew, it might shed light on either one.”

The detective grinned and changed the subject. “Right now, I want you all to come for a drive and have a look at the boys’ surprise.”

“Swell!” Frank and Joe exclaimed in unison.

While Aunt Gertrude and Mrs. Hardy were getting ready, Frank and Joe went out to the car with their father. Quickly the boys related their afternoon’s experience, concluding with the arrow incident.

The detective looked grim. “Whoever is responsible for these warnings is certainly keeping close tabs on us.”

Mr. Hardy and his sons speculated for a few minutes on the fact that the pedal found in front of the house apparently had belonged to Ken’s bike.

“I think Joe and I should go back tonight to the place where we had the picnic,” Frank told his father. “In the darkness we’ll have a better chance to sleuth without being seen. And there might be some clue we missed this afternoon.”

“I suppose you’re right,” agreed his father. “But be cautious.”

As Aunt Gertrude and Mrs. Hardy came out of the house, conversation about the mystery ceased.

Everyone climbed into the sedan and Mr. Hardy drove off. Frank and Joe, seated alongside him, were in a state of rising suspense. Was the surprise the one thing they wanted most of all? CHAPTER VIII The Strange Mill Wheel

A FEW minutes later Mr. Hardy was driving along the Bayport waterfront.

“Is the surprise here, Dad?” Joe asked excitedly.

“That’s right.”

Mr. Hardy drove to a boathouse at the far end of the dock area and parked. He then invited the others to follow him. He walked to the door of a boathouse and unfastened the padlock.

Frank and Joe held their breaths as Mr. Hardy swung back the door. For a moment they stared inside, speechless with delight. Finally Joe burst out, “Exactly what we had hoped for, Dad!” and put an arm affectionately around his father.

“What a beauty!” Frank exclaimed and wrung Mr. Hardy’s hand.

Rocking between the piles lay a sleek, completely equipped motorboat. It nudged gently against clean white fenders as the waves from the bay worked their way under the boathouse door.

The boys’ mother exclaimed in delight, and even Aunt Gertrude was duly impressed by the handsome craft.

“This is the same model we saw at the boat show,” Joe said admiringly. “I never thought we’d own one.”

“She even has the name we picked out,” Frank observed excitedly. “The Sleuth!”

Shiny brass letters were fitted on the bow of the boat, with the port of registry, Bayport, underneath them.

Mr. Hardy and his wife beamed as their sons walked up and down, praising every detail of the graceful new craft. It could seat six people comfortably. The polished fore and aft decks carried gleaming anchor fittings, and the rubbing strakes were painted white. The Sleuth seemed to be waiting to be taken for a run!

“May we try her out now, Dad?” Joe asked.

“Of course. She’s fueled up.”

Aunt Gertrude shook her head. “The Sleuth’s an attractive boat, all right. But don’t you two start doing any crazy stunts in it,” she cautioned her nephews. “And be back for supper.”

When the adults had left, Frank and Joe climbed aboard and soon had the Sleuth gliding into the bay.

The boys had no difficulty operating the motorboat. They had gained experience running their friend Tony Prito’s boat, the Napoli, which had similar controls.

Taking turns at the wheel, the brothers ran the boat up and down the bay. “Terrific!” Joe shouted.Frank grinned. “Am I glad we stuck to our agreement with Dad, and saved up to help buy this!”

For some time the boys had been putting money toward a boat of their own into a special bank account.

Mr. Hardy had promised that when the account reached a certain sum, he would make up the necessary balance.

Now, as the Sleuth knifed through the water, Frank and Joe admired the way the stern sat down in the water when the boat gathered speed. Joe was impressed with the turning circle and the fact that no matter how sharp the twist, none of the spume sprayed into the cockpit.

“Wait until Tony and Chet see this!” Joe exclaimed, when they were pulling back toward the boathouse.

“Speaking of Tony-there he is,” Frank said. Their dark-haired classmate was standing on the dock, shouting and waving to them.

Joe, who was at the wheel, brought the Sleuth neatly alongside. He turned off the engine as Tony rushed up.

“Don’t tell me this dreamboat is yours?” he demanded in amazement.

“Nothing but,” Joe said proudly.

Tony and the brothers inspected the boat carefully, comparing her various features with the Napoli, They lifted the battens from the Sleuth’s cowling and admired the powerful motor underneath.

“She’s neat all right,” said Tony. “But I’ll still promise you a stiff race in the Napoli!”

“We’ll take you up on it after the Sleuth’s broken in,” Joe returned, laughing.

Tony became serious. “Say, fellows, something happened today in connection with my dad’s business that I want to tell you about. Your mother said you were down here,” he explained.

“What’s up?” Frank asked.

Tony’s father was a building contractor and also had a construction supply yard where Tony worked during the summer. “Today I went to the bank, just before it closed, to deposit the cash and checks we took in this week,” he said. “The teller discovered that one of the bills was a counterfeit!”

“A twenty-dollar bill?” Frank guessed.

“Yes. How’d you know?”

The Hardys related Chet’s experience. Tony’s dark brows drew together. “I’d like to get my hands on the guy making the stuff!” he said angrily.

“So would we!” Joe stated.

The Hardys learned that the head teller had told Tony he would make a report to the Bayport police and turn the bill over to the Secret Service, “Did he explain how he could tell that the bill was a fake?” Frank asked.

“Yes,” replied Tony, and from his description, the Hardys were sure that the bill had come from the same batch as the one passed to Chet.

“Think back, Tony,” Frank urged. “Have you any idea who gave it to you-or your father?”Tony looked doubtful. “Three days’ trade- pretty hard to remember. Of course, we know most of the customers. I did ask Mike, our yardman, who helps with sales. He mentioned one purchaser he didn’t know.”

Frank, eager for any possible lead, carefully questioned Tony. The Hardys learned that three days before, just at closing time, a faded green panel truck had driven into the Prito supply yard. “Mike remembers there were no markings on the truck-as if the name might have been painted out.”

“Who was in it?” Joe prompted.

“A young boy-about fourteen-was with the driver, Mike says they bought about fifty dollars’ worth of old bricks and lumber. The boy paid him in assorted bills. One was a twenty. Our other cash customers had given smaller bills.”

“What did the driver look like?” Frank probed.

“Mike said he didn’t notice-the fellow stayed behind the wheel. There was a last-minute rush at the yard, so the boy and Mike piled the stuff into the back of the truck. Then the driver gave the boy money to pay the bill.”

Frank and Joe wondered the same thing: Had the man driving the truck passed the bogus bill deliberately? If so, was he the one who had fooled Chet? “It seems funny he’d go to so much trouble to dump one phony twenty-dollar bill,” Joe said.

Frank agreed and added, “Besides, what would a person in league with counterfeiters want with a pile of old bricks and lumber?”

He turned to Tony. “Did Mike notice anything in particular about the boy?”

“He was tall and thin. Mike thinks he was wearing a striped shirt.”

Frank and Joe exchanged glances. “Could be Ken Blake!” Joe declared. Briefly, the Hardys explained their first encounter with the boy.

“He might have been helping pick up the load for Elekton,” Frank reasoned. “But why would a modern plant want secondhand building material? And why wouldn’t they have the purchase billed to them?”

“What’s more,” his brother put in, “why didn’t the driver get out and help with the loading? Unless, perhaps, he wanted to stay out of sight as much as possible.”

“Too bad Mike didn’t notice the truck’s license number,” Tony said. “Naturally he had no reason to at the time.”

“Was there anything unusual about the truck besides the fact it wasn’t marked?” Frank asked his chum.

Tony thought for a moment. “Mike did say there was a bike in the back. He had to move it out of the way.”

“Ken rides one,” Joe remarked.

“Well, Dad will be glad if you two pick up any clues to these counterfeiters,” Tony said. “He’s hopping mad at being cheated, and Mike feels sore about it.”

“We’ll keep our eyes open for that green truck,” Frank assured him. “The whole business sounds suspicious-though the bill could have been passed accidentally.”“Let’s question Ken Blake,” Joe proposed.

He and his brother housed the Sleuth, and the three boys started homeward. On the way they continued to speculate on the counterfeiting racket.

“Let me know if I can help you detectives,” Tony said as he turned into his street.

“Will do.”

That evening, when it grew dark, Frank and Joe told their mother and aunt that they were going out to do some investigating. Before they left, the boys had a chance to speak to their father in private about Tony’s report of the counterfeit bill and green truck and their own hunches.

Mr. Hardy agreed that the purchase of lumber and bricks seemed odd, but he felt that until more positive evidence could be obtained, it was best not to approach Elekton officials on the matter.

“I guess you’re right, Dad,” said Frank. “We might be way off base.”

The detective wished them luck on their sleuthing mission. The boys decided to make the trip in the Sleuth. They rode their motorcycles down to the boathouse, parked them, then climbed aboard the new boat. Joe took the wheel and soon the sleek craft was cutting across the bay toward the mouth of Willow River.

When they entered it, Joe throttled down and carefully navigated the stream. Meanwhile, Frank shone his flashlight on the wooded banks.

“There’s the cave-ahead!” he whispered.

Joe ran the boat astern a few yards and Frank dropped anchor. The brothers waded ashore, carrying their shoes and socks.

When they reached the mouth of the cave, Joe said, “Let’s investigate this place first.”

They went into the cave and moved forward to the tunnel. One glance told them that the tunnel had become impassable-it was filled with water.

“Must have been the cloudburst,” said Frank, as they emerged from the cave. “We’ll have to wait until the ground dries out. At least we can take a look through the woods and the area around the mill for clues to the bowman.”

Shielding the lenses of their flashlights, so that the light beams would not be easily detected by anyone lurking in the vicinity, the boys began a thorough search of the wooded section. As they worked their way noiselessly uphill among the trees, the only sound was the eerie rattling the wind made in the leaves and branches.

Frank and Joe shone their lights beneath shrubs and rocks, and even crawled under some fallen trees.

They found nothing suspicious. They were approaching the edge of the woods and could see the outline of the mill beyond. The old wheel creaked and rumbled.

Suddenly Frank whispered hoarsely, “Look! Here’s something!”

Joe joined his brother, and together they examined the leather object Frank had picked up.

“An archer’s finger guard,” he said.”It may be a valuable clue to the arrow warning,” Joe said, as Frank pocketed the guard. “Let’s go up to the mill,” he proposed. “Maybe the men there have seen something suspicious.”

As the boys crossed the clearing toward the gatehouse, they saw that it was in darkness.

“Probably everyone has gone to bed,” Frank remarked.

For a moment the brothers stood wondering what to do next. “Something’s missing,” Joe said in a puzzled voice. “I have it! The mill wheel has stopped turning.”

“Maybe it was switched off for the night,” Frank observed.

The boys were eager to question the occupants, but decided not to awaken them.

“Let’s walk around the mill,” said Frank, “and look through the woods on the other side.”

The boys had just passed the north corner of the building when, with a creaking groan, the wheel started to turn again.

“There must be something wrong with the mechanism,” Frank deduced. “The wheel hasn’t been used for so many years that adapting it to work the generator may have put a strain on it.”

“We’d better let the men know it’s acting up,” Joe said.

The boys retraced their steps to the mill door. As they reached it, the wheel stopped turning.

Frank and Joe stood staring off to their left where the mass of the motionless wheel was outlined against the night sky.

“Spooky, isn’t it?” Joe commented.

Frank nodded, and knocked on the door. There was no response. After a short wait, he knocked again-louder this time. The sound echoed in the deep silence of the night. Still no one answered.

The Hardys waited a while longer. Finally they turned away. “Must be sound sleepers,” Joe commented.

“Well, maybe they’ll discover what’s wrong tomorrow.”

Frank and Joe were about to resume their search for clues when they heard a loud crashing noise from the woods which bordered Willow River.

The boys dashed ahead to investigate. Entering the woods, they made their way stealthily forward, flashlights turned off. Silently they drew near the river.

After a few minutes they stopped, and listened intently. The sound was not repeated.

“Must have been an animal,” Joe whispered.

Just then they heard a rustling sound behind them and turned to look. The next instant each received a terrific blow on the back of the head. Both boys blacked out.

CHAPTER IXTracing a Slugger

WHEN Frank regained consciousness, his first thought was of his brother. He turned his throbbing head and saw that Joe was lying next to him.

“Joe!” he exclaimed anxiously.

To his relief, Joe stirred and mumbled, “W-what happened?”

“Someone conked us on the head-“

Frank broke off as he became aware of a gentle rocking motion. He sat up. Was he still dizzy or were they moving? When his mind and vision cleared, he knew they were certainly moving.

“Hey!” he said. “We’re on the Sleuth!”

Astonished, Joe raised himself and looked around. They were indeed aboard their boat- lying on the foredeck and slowly drifting down Willow River toward the bay. The anchor lay beside them.

“A fog’s rolling in,” Frank said uneasily, observing white swirls of mist ahead. “Let’s start ‘er up before visibility gets worse.”

The boys wriggled into the cockpit and Joe pressed the starter. It would not catch. While Joe stayed at the controls, Frank climbed to the foredeck and lifted the cowling from the engine. He quickly checked to see if the distributor wires were in place. They were. There did not seem to be anything visibly wrong with the engine, but when he lifted the top off the carburetor, he found it empty.

A quick check of the gas tank revealed the cause of the trouble. The tank had been drained.

“Fine mess we’re in,” he mumbled. “What was the idea?”

“The man who hit us on the head can answer that one,” Joe said bitterly. “He sure did a complete job-even took both the oars!”

“We’ll have to tow her,” Frank said tersely, “to make more speed and guide her,”

While Joe stripped to his shorts, Frank quickly led a painter through one of the foredeck fair-leads.

“Take this painter,” Frank said, handing Joe the rope. “Make it fast around your shoulder and swim straight ahead. I’ll unhinge one of the battens and use it as a paddle and try to keep her straight. In a few minutes I’ll change places with you.”

The Hardys knew that keeping a dead weight like the Sleuth moving in a straight line would be a tough job. However, with Joe swimming ahead and Frank wielding the batten, they managed to make fairly steady progress.

It was slow, backbreaking work, and before they reached the bay, the boys had changed places three times. Their heads were pounding more than ever from the physical strain. Also, the fog had grown so dense that it was impossible to see very far ahead.

Frank, who was taking his turn in the water, did not know how much longer he could go on.

Suddenly Joe shouted from the boat, “There’s a light! Help! Help! Ahoy! Over here!” he directed at the top of his lungs.Gradually the light approached them. Frank clambered back into the Sleuth as a Harbor Police boat, making its scheduled rounds, pulled alongside.

“You’re just in time!” Frank gasped to the sergeant in charge. “We’re exhausted.”

“I can see that. You run out of gas?” the police officer asked.

“Worse than that. Foul play,” Frank replied.

“Tough luck,” the sergeant said. “You can tell your story when we get to town.”

The officer gave orders to his crew, and a tow-line was put on the Sleuth. The boys were given blankets to throw around themselves.

When the two crafts reached the Harbor Police pier, the boys went inside and gave a full account of what had happened to them and asked that the report be relayed to Chief Collig.

“We’ll give you some gas,” said the sergeant who had rescued the boys. “Then do you think you can make it home alone?”

“Yes, thank you.”

A half hour later the boys, tired and disappointed, cycled home. Their mother and aunt gasped with dismay at the sight of the weary boys in the water-sodden clothing. Joe and Frank, however, made light of the evening’s experience.

“We ran out of gas,” Joe explained, “and had to swim back with the Sleuth”

Aunt Gertrude sniffed skeptically. “Humph! It must have been some long ride to use up all that fuel!” She hustled off to make hot chocolate.

Mrs. Hardy told the boys that their father had left the house an hour before and would be away overnight working on his case. Again Frank and Joe wondered about it. And did the attack tonight have any connection with either case?

After a hot bath and a good night’s sleep, Frank and Joe were eager to continue their search for clues to the bowman, the counterfeiters, and the writer of the first warning note to Mr. Hardy.

Breakfast over, Frank and Joe went to the lab and dusted the archer’s finger guard. To the brothers’

delight they lifted one clear print.

“We’ll take this to Chief Collig on our way to the paper company in Bridgeport,” Frank decided.

Just before they left, Chet telephoned. “Guess what!” he said to Frank, who answered. “I have an appointment at Elekton to see about a job!”

“How’d you do it?” Frank asked, amazed. “You sure work fast.”

Chet laughed. “I decided to telephone on my own,” he explained. “The man in the personnel office told me there might be something available on a part-time basis. How about that?”

“Swell,” Frank said. “The vacancy must have come up since yesterday.”

“Funny thing,” Chet added, “The personnel manager asked me if I’d applied before. I said No, though the guard had phoned about me yesterday. The manager said he didn’t remember this, but that somebodyelse in the office might have taken the call.”

Chet became more and more excited as he talked about the prospect of getting a job in the Elekton laboratory. “I’m going to make a lot of money and-“

“Don’t get your hopes up too high,” Frank cautioned his friend. “Elekton is such a top-secret outfit they might not hire anyone on a part-time basis for lab work. But you might get something else.”

“Well see,” Chet replied optimistically.

“Joe and I have something special to show you,” Frank told him. “After you have your interview, meet us at the north end of the Bayport waterfront.”

Chet begged to know why, but Frank kept the news about the Sleuth a secret, “You’ll see soon enough,”

he said.

“Okay, then. So long!”

The Hardys hopped on their motorcycles and rode to police headquarters. They talked to Chief Collig in detail about the attack on them, and left the bowman’s fingerprint for him to trace.

“Good work, boys,” he said. “I’ll let you know what I find out.”

Frank and Joe had decided not to mention to him the green truck and its possible connection with the counterfeiters until they had more proof.

The boys mounted their motorcycles and rode to Bridgeport. They easily located the Quality Paper Company, and inquired there for Mr. Evans, the sales manager, with whom they had talked the day before.

When Frank and Joe entered his office and identified themselves, Mr. Evans looked at the brothers curiously. But he was most cooperative in answering their questions.

“No,” Mr. Evans said, “we don’t sell our star watermark paper to retail stores in this vicinity. All our purchasers are large industrial companies. Here is a list.” He handed a printed sheet across the desk to Frank.

The boys were disappointed not to have obtained any individual’s name. Nevertheless, Frank and Joe read the list carefully. Several names, including Elekton Controls Limited, were familiar to them. The warning note could have come from any one of thousands of employees of any of the firms.

“I guess there’s no clue here to the man we want to locate,” Frank said to Mr. Evans.

The boys thanked him. As they started to leave, he called them back.

“Are you boys, by any chance, related to Mr. Fenton Hardy?” he asked.

Joe, puzzled, nodded. “He’s our father. Why?”

“Quite a coincidence,” Mr, Evans said. “Mr. Hardy was here a little while ago.”

“He was!” Frank exclaimed in surprise. The brothers exchanged glances, wondering what mission their father had been on.

“Maybe I shouldn’t have mentioned Mr. Hardy’s visit,” Mr. Evans said.”That’s all right,” Joe assured him. “If Dad had wanted the visit kept secret, he would have told you.”

When the boys were outside again, Frank said, “I hope Dad will be home. I’d like to find out what brought him here.”

Frank and Joe rode directly home and were glad to see Mr. Hardy’s sedan in the driveway. The boys rushed into the house.

They found the detective in his study, talking on the telephone. The boys paused next to the partly open door.

”. . . the same eight-and-one pattern, I believe,” their father was saying. . . . “Yes-I’ll be there. . . . Good-by.”

Frank knocked and the boys entered the room. Mr. Hardy greeted them warmly. He was startled when Joe told him, “We know where you’ve been this morning, Dad.”

“Were you two shadowing me?” the detective joked.

“Not exactly.” Frank grinned, and explained why they had visited the Quality Paper Company.

“Good idea,” said the detective. “Did you learn anything?”

“No,” Joe replied glumly, then asked suddenly, “Dad, did you go to Quality Paper in connection with the warning note on the arrow?”

Mr. Hardy admitted that he had gone there to investigate the watermark. “I believe I did find a clue to confirm a suspicion of mine. But I’m not sure yet where it will lead.”

The boys sensed that their father’s trip had been linked to his secret case. “If it was to help us on the counterfeiting mystery, he’d say so,” Frank thought. “And he hasn’t mentioned Elekton, so I guess he doesn’t suspect any of that company’s employees.”

Mr. Hardy changed the subject. He looked at his sons quizzically. “What’s this I hear from Aunt Gertrude about you boys coming home last night half dead?”

The boys explained, omitting none of the details. “We didn’t want to alarm Mother and Aunt Gertrude,”

Frank said, “so we didn’t tell them about the attack.”

Mr. Hardy looked grim and warned his sons gravely to be extra cautious.

“There’s one bright spot,” he added. “The print you found on that finger guard. It could be a big break.”

During lunch the detective was unusually preoccupied. The boys tried to draw him out by questions and deductions about the counterfeiting case. He would say very little, however, and seemed to be concentrating on a knotty problem.

A little later the boys rode their motorcycles straight to the boathouse and parked at the street end of the jetty. “Chet ought to show up soon,” Joe remarked.

As the brothers walked toward the boathouse Frank commented on his father’s preoccupation during luncheon.

“I have a hunch Dad’s assignment is even tougher than usual,” he confided. “I wish we could help him on it.”Frank seemed to be only half listening and nodded absently.

“What’s the matter with you?” Joe laughed. “I’m talking to myself!”

Suddenly Frank stopped. He grasped his brother’s arm firmly.

“Joe!” he said. “We may have found a clue in Bridgeport this morning, and didn’t realize it!”

CHAPTER X

The Sign of the Arrow

“WHAT clue do you mean, Frank?” Joe demanded eagerly.

“Elekton’s name was on that list Mr. Evans showed us this morning.”

“Yes, I know. But Dad didn’t seem excited over that.”

“Well, I am,” Frank said. “Put two and two together. Every time we’ve been near the Elekton area, something has happened. First, the warning on the arrow, then the attack last night.”

“Of course!” Joe said. “I get you! Someone who has access to the company’s paper supply could have sent the warnings, and knocked us out. But who? An employee of Elekton?”

“That’s the mystery,” said Frank. “Is the person trying to get at Dad through us? And which of the cases is this mysterious person connected with ‘-the counterfeit case or Dad’s secret one?”

“Then there’s the bike,” Joe recalled. “Someone from the company easily could have taken it from the storage area under the mill at night when the guard and maintenance man were inside the gatehouse.”

“Joe,” said Frank slowly, “we’re theorizing on the case having a connection with Elekton. Do you think Dad is, too, even though he didn’t tell us? The Elekton name may have been the clue he found at Quality Paper!”

Joe snapped his fingers. “My guess is that Dad is doing some detective work for Elekton! That would explain why he can’t say anything. Elekton is doing top-secret space missile work.”

“It’s possible,” Frank speculated, “that Elekton retained Dad because of the chain of sabotage acts in plants handling similar jobs for the government.”

“Sounds logical,” Joe agreed. “I guess Dad’s main assignment would be to ward off sabotage at Elekton.

No wonder he is so anxious to find out who sent the warnings.”

Just then Chet arrived in the Queen and leaped out.

“I have a job!” he announced to Frank and Joe. Then he looked a bit sheepish. “It’s-er-in the cafeteria, serving behind the food counter. The cafeteria is run on a concession basis, and the people working there aren’t as carefully screened as the plant employees.”

Joe grinned. “It’s not very scientific, but think of the food! You’ll be able to eat anything you want.”Chet sighed, and did not respond with one of his usual humorous comebacks. A worried expression spread over his face. He shifted from one foot to the other.

“What’s on your mind?” Joe prodded. “Not nervous about the job, are you?”

Chet shook his head. He dug into his pocket and pulled out a piece of white paper. “I am nervous about this-another warning note! It was on the seat of my car when I came out after the job interview.” He handed the note to Frank.

Unfolding it, Frank read aloud, “ ‘You and your pals watch out!’ “ There was no signature on the boldly printed note, but at the bottom was the crude drawing of an arrow.

Chet gulped. “Must be that arrow shooter. He’s keeping tabs on all of us!” he said.

Frank and Joe studied the note intently for a minute, then Frank asked Chet, “Where did you park?”

“Near the front entrance. The guard at the mill told me to go in that way to reach the personnel office.”

Chet smiled faintly. “Boy, was he surprised when I told him I had an appointment.”

The Hardys were more convinced than ever that their unknown enemy must somehow be linked with the Elekton company. “We’ll compare this note with the others,” Frank said. “But first, Chet, we’ll show you something to cheer you up.”

The brothers led their friend into the boat-house. “Feast your eyes!” Joe grinned. “This is our surprise.”

Chet gasped when he saw the Sleuth. “Wow! She’s really yours?”

“You bet! How about a ride?”

Eagerly Chet accepted. As the Hardys refueled from the boathouse tank, they told Chet about the adventure they had had the previous night.

“You suspect there’s a connection between somebody at Elekton and the counterfeiting?” Chet guessed.

“That’s right,” Frank replied.

He then told Chet about the Pritos having received a counterfeit bill, “We think,” said Joe, “the boy in the panel truck who gave Mike the counterfeit twenty might have been Ken Blake,”

“Ken Blake again,” Chet commented. “Funny how he keeps turning up.”

The Hardys agreed. As Frank steered the Sleuth into the bay, Joe suggested, “Let’s run up Willow River to the mill. That’ll give you a good chance to see how the boat rides, Chet, and also we can stop to question the guard and maintenance man, and Ken Blake. They might have seen some suspicious people in the area.”

“I should’ve known this would turn into a sleuthing trip.” Chet sighed. “Oh, well, I’m with you if we can learn anything about the counterfeiters.”

When Frank had the Sleuth well away from shore and out of the path of other craft on the bay, he pushed the throttle for more speed and steered the boat toward the mouth of the river.

The Sleuth responded like a thoroughbred. The stern sat back in the water and in a second it was planing wide open across the bay.”How do you like this?” Frank called from the cockpit.

“Terrific!” Chet yelled back enthusiastically.

Frank now swung the wheel back and forth to show his friend how stable the boat was. Then he said, “Joe, take the wheel and show Chet your stuff!”

The brothers changed places and Joe made a wide circle to port, with the Sleuth heeling beautifully. Then he headed for the river’s narrow mouth.

“Better slow down!” Frank warned him.

Obediently Joe began to ease the throttle. The Sleuth did not respond! And there was no lessening of the roar of the engine.

Quickly Joe turned the throttle all the way back. Still there was no decrease in speed.

“Something’s wrong!” he shouted. “I can’t slow her down!”