“This is a good setup here,” Barto remarked. “Too bad we have to leave it.”
“Now that we have the experimental motor,” Vilno put in, “there's no reason for us to stick around.”
“What about the prisoners?” Dodson inquired. “Alden and his son don't worry me, but that detective Hardy can be dangerous to us.”
Frank and Joe gasped. Their father had been captured together with Mr. Alden and Roger!
“Forget it,” Vilno told Dodson. “We'll be miles away before anyone finds Hardy.”
Frank turned to his brother. “We must rescue them!”
“We can't do it alone! There are probably more members of the gang inside.”
Suddenly the tall figure of a man loomed up behind the boys. “Who are you?” he demanded.
Frank and Joe leaped to defend themselves. A wild struggle followed. They crashed against the side of the house several times. Then Frank dealt the man a blow that sent him crumbling to the ground.
Suddenly the young detectives heard another, but louder, humming sound. In the next instant they were horror-stricken to find that they could not move.
“What's happening?” Joe exclaimed.
The boys were frozen in their tracks. Some powerful, invisible force was holding them!
CHAPTER XX
Jet Action
“IT'S THE Hardy kids!” Dodson shouted as he, Barto, and two other men arrived on the scene.
“Don't get too close to them,” Barto warned his pals, “or you'll get caught in the sonic trap yourselves. Tadlow! Go tell my brother to turn it off.”
Within a couple of minutes the boys were released from the mysterious force that had prevented them from moving. The aftereffects, however, caused Frank and Joe to fall to the ground exhausted. Dodson and the others pounced on them and tied the boys' hands behind their backs.
“So! How do you like our little sonic trap?” Barto sneered.
“Sonic trap?” Frank said weakly.
“Yes,” Barto replied. “It's another of Vilno's inventions. A device which encloses objects of our choosing within a solid shell of hypersonic vibrations. Your father also had the honor of experiencing its effects.”
Frank and Joe were marched into the mansion, then down a flight of stairs leading to the basement. They were awed by what they saw. The area had been converted into a large laboratory, and was filled with various pieces of electronic equipment. In one corner of the room lay several signposts marked DANGER.
“Welcome! Welcome!” Vilno exclaimed with exaggerated politeness. “Looking for your father? Well, you've come to the right place.”
“If you've harmed him,” Joe began, “or ...”
“He's perfectly fit,” Vilno interrupted, “and is in our storage room with Alden and his son. You shall join them shortly.”
For the first time the boys had an opportunity to see Vilno and Barto together. They were identical twins. Other than for a difference in dress, it was difficult to tell who was who.
“Perhaps our guests would like to see some of the things we invented,” Barto sneered.
“That
we
invented? You're forgetting it was my genius alone that made our devices possible!” his twin said boastfully.
“How did you manage to craze the windshields of Mr. Alden's race cars?” Frank interjected.
Vilno seemed pleased by the question. He led the Hardys to the signposts. “Inside each of these is a hypersonic generator of my own design. I found that I could disturb the molecular arrangement in some materials with the waves it produces. They are what crazed the windshields of Alden's cars.”
“And the windows of our plane!” Joe said angrily.
“Ah yes,” Vilno said. A sinister smile spread across his face. He walked to a table and picked up a long, cylindrical object. “Your plane was among the first objects on which I tried the portable version of the hypersonic generator.”
“Then it was you, and not Barto, who stole Mr. Alden's experimental car,” Frank remarked.
“Precisely,” Vilno replied.
At that moment Barto began to roar with laughter. “They still don't know,” he told his brother, “that it was you who was working at the plant all the time, posing as me!”
“But how could you carry on the deception?” Joe sputtered. “You're not a sheet-metal worker.”
“That's where you're wrong,” Vilno shot back. “My brother and I were both trained in sheet-metal work as youths. But I never claimed it as one of my skills. My ambition was to become a scientist.”
“Why are we standing around here talking?” Dodson said impatiently. “These snoopers might have told the police they were coming here!”
“Then where are they?” Vilno countered. “You worry too much.”
“I don't care what you say!” Dodson retorted. “I ... ”
“Shut up!” Barto broke in. “We should've let you stay in jail for stealing Alden's race horse. Why did you do it? Aren't we paying you enough?”
“And your stupidity didn't end with the horse theft,” Vilno added with a touch of irritation. “You made the mistake of telephoning me at my apartment from Haversville Police Headquarters. Idiotl I knew the Hardys were bound to check the number.”
Dodson grimaced but said, “You're not so smart. You started a fire in the experimental lab.”
Frank broke in. “Vilno, you say you were posing as your brother all the time. Yet it was Barto's fingerprints I found on the doorknob of your apartment the day I followed you home from the plant.”
“Quite simple,” Vilno answered proudly. “Barto and I were dressed exactly alike and switched places in the lobby. It was he you saw enter the apartment.”
“But how did you know you were going to be followed that day?” Joe asked quickly.
“Your taking summer jobs at the plant didn't fool us,” Barto put in. “We knew you were probably investigating the Alden case. Vilno guessed that he would be a suspect, and that you would undoubtedly shadow him. So, each day, we wore similar clothes in the event we had to switch places. The plan paid off. You followed the wrong one on the street in Clayton. Vilno pretended a friend was a bum and shoved him away.”
“We've told them enough,” Vilno growled. “Put them in the storage room with the others.”
Dodson and two men marched Frank and Joe out of the laboratory and down a narrow passageway. They came to a stop in front of a heavy metal door. Dodson pulled it open.
“Inside!” he ordered.
The boys entered a small, windowless room made of stone. Before the door was closed, they saw their father, Alden, and Roger.
“Dad!” Joe exclaimed.
“I see you two also had some bad luck,” the detective said remorsefully.
The metal door clanged shut and the Hardys and their companions were in total darkness.
“We were surprised to learn that you and Mr. Alden had been captured, Dad,” Frank remarked.
“I walked into Vilno's sonic trap,” Mr. Hardy explained.
“How did you find the gang's hideout?” Joe asked.
“After you left Mr. Alden's office, I went to Clayton Police Station in Mr. Alden's car to tell them about the situation, and to arrange for help in case we needed it. I planned to return to the plant in time for Vilno's telephone call. When I was driving back, I saw Mr. Alden go by me from the opposite direction in a truck.”
“Sorry about that.” The executive sighed. “This is how it happened, boys. Vilno called me again shortly after your father left. He told me he'd been watching the plant and saw Mr. Hardy drive off. Vilno was worried he was going to the police and demanded I deliver the experimental motor to him immediately. For Roger's sake, I had no choice.”
“What happened then?” Frank asked.
“Vilno ordered me to bring the motor to the Bryant crossroads north of Clayton,” Mr. Alden replied. “There, two of his men jumped into the truck with me and told me to drive on. We came here to the mansion.”
“I followed the truck,” Mr. Hardy interjected. “Too bad I didn't have my own car, or I would have contacted you boys by radio. And unfortunately I couldn't stop to use a telephone.”
“You people wouldn't be in this mess if it wasn't for me,” Roger muttered.
Frank began to grope around their enclosure, hoping for a way of escape. His father said, “The walls are solid, and you couldn't budge that metal door with a bulldozer.”
“The room is completely sealed,” Mr. Alden added, “except for an air vent. Thank goodness for that.”
“Air vent,” Frank repeated, looking for it.
“It's near the ceiling,” Mr. Hardy said. “But if you're thinking of an escape route, it's too small for any of us to crawl through.”
“Let me try,” Joe urged. “I've managed to squeeze through some pretty small spaces before.”
Mr. Hardy guided his sons to the rear wall of the room. “The vent should be directly above this spot.”
Frank hoisted his brother onto his shoulders. Joe ran one hand along the upper portion of the wall. “I've found it! The vent is covered with a metal grating.” There was a momentary pause. “I think I can pull it loose.”
Joe tugged the grating hard. Finally it broke free of the wall. “The opening is small, but I'm sure I can manage to get through. Boost me up higher.”
Frank grabbed his brother's feet with both hands and shoved him upward. An instant later Joe was gone.
“Be careful, son,” Mr. Hardy called.
But Joe was not free yet. He was in an air duct. His arms stretched out in front of him, Joe forced his way through the narrow passageway. Minutes seemed like hours. Finally he was elated to find that the vent led directly outside the mansion.
Another grating, however, barred his way. He grasped the bars with both hands and shoved with all his strength. The grating loosened and dropped outside to the ground.
After climbing out of the vent, Joe scanned his surroundings. Several yards away he saw Vilno and his henchmen preparing to depart in Alden's truck.
Stealthily, the young detective stalked toward the front door of the mansion. Luckily it was unlocked. He raced inside and ran down to the storage room to free his companions.
“Quick! Vilno and his men are getting ready to leave!”
The three Hardys and their friends rushed outside the mansion. They were crestfallen to see that the truck had already pulled away.
“We'll never catch them!” Frank declared.
“Look!” Joe yelled. “What's that glow?”
His companions were startled to see a bright ball of light approaching the truck head-on. Just as a collision seemed imminent, the vehicle veered off the lane. This was followed by a loud crunching sound.
“What's that?” Alden shouted.
They detected a roar as the glow grew closer. Then it suddenly vanished. Seconds later Chet Morton coasted out of the darkness on his jet-propelled bicycle.
“Hi, fellows! Am I glad to see you!”
“Chet! What are you doing here?” Frank exclaimed.
“I began to worry when I didn't hear from you,” the chubby youth explained. “So did your mother and aunt. I decided to see what was going on. My car ran out of gas about a mile from here, so I came the rest of the way on my jet bike.” His eyes widened. “By the way, I almost ran into a truck! What happened to it?”
The Hardys hurried to the spot where they had seen the vehicle veer off the lane. They found it tightly wedged between two stout trees. Vilno and his pals were desperately trying to open the doors but without success.
Just then a State Police car arrived on the scene. One of the troopers got out. “Did any of you see a wild kid on a bicycle?” he questioned. “We think it turned in here. Looked as if it was on fire.”
“I'm the one,” Chet admitted sheepishly.
“What were you trying to do?” the officer demanded. “You went by us as if you'd been shot out of a cannon.” His attention was attracted by the disabled truck. “What happened here? Accident?”
Mr. Hardy stepped forward. “Let me explain,” he said.
After hearing the story, the officer radioed for additional men, then the troopers took Vilno and his henchmen into custody.
“We'd have escaped if it hadn't been for that crazy friend of yours and his bicycle,” the gang leader growled.
“That's your hard luck!” Joe told him.
Mr. Hardy said, “We know that specifications of Mr. Alden's motor were leaking out of the plant. How did you manage it?”
Vilno's egotism caused him to forget his predicament for a moment. “Easy! Alden's machinists worked from plans recorded on film slides. I just roamed around the plant and photographed the projected pictures with a spy camera in my wrist watch. Other components I committed to memory and put them down on paper later.”
Soon more troopers arrived. The prisoners were herded into patrol cars. The case of
The Sinister Signpost
was over. Frank and Joe always regretted such a moment. They were not restless for long, however, because the mystery of A
Figure in Hiding
soon came their way.
Before departing, one of the officers walked up to Chet. “I should give you a ticket for speeding,” he announced, winking at the Hardys.
“IâI wish you wouldn't,” Chet stammered, “It won't happen again.”
“Well, under the circumstances, I think I can overlook it this time.” The trooper sighed, trying not to grin. “Anyway, I wouldn't know how to describe your jet-propelled bike to the judge,”
“We warned you about that invention of yours,” Joe whispered, nudging his chum, “Lucky for us you didn't listen!”