Bud had raced from the control house to help the technicians who were attempting to knock down the giant. But Ator remained upright, keeping his balance, despite the combined weight pushing against him. Several men jumped into the air trying to grab Mr. Swift, but none of them could reach him. The robot held on tightly.

By this time, Ator was beginning to close both arms around his helpless victim. That viselike grip, Tom knew, would crush his father!

CHAPTER 24.

THE GIANTS CLASH.

IN DESPERATION Tom abandoned his struggle to control Ator, realizing there was only one remaining chance: Sermek!

Turning to the second robot's warmed-up control panel, he sliced down a series of knife switches, spun the dials, and Sermek strode into action, bearing down upon the first giant robot.

Ator seemed to sense the impending danger. The mechanical giant clanked to a halt, lowered his captive, and relaxed the iron-clad grip. Struggling to release himself, Mr. Swift fell free and scrambled to his feet. Bud was there instantly to help him to safety.

Turning, Ator advanced toward Sermek and the automatons circled each other warily. Ator's right hand contracted into the equivalent of a fist and his arm stiffened into a lance. He charged as Sermek braced his feet against the earth.

194.

THE GIANTS CLASH 195.

The giants collided with a crash that resounded deafeningly through the grounds. Tom fully realized the gravity of the situation. The hidden hand manipulating Ator seemed bent on an all-out battle without regard for the possible destruction of both robots. Somehow he must deactivate Ator's controls without permanent injury to either robot.

Ator backed off and began to stalk his opponent, looking for an opening.

Then, pivoting quickly, he lunged forward. Sermek side-stepped, but not far enough to avoid a smash in the face that damaged his control circuits, stiffening the joints in one leg. The robot jockeyed awkwardly for position. Two more blows shook his eye circuits.

Tom worked feverishly to compensate for the distortion. If Sermek was to win now, Tom knew, the battle would have to end rapidly.

He switched to wrestling techniques. A clanging din filled the air as each giant fought for a hold on the other's vulnerable head mechanism. A contest of strategy, not strength, was exactly what Tom wanted. Now he could use scientific tactics based on his knowledge of the robot's structural operations.

For a moment Ator had the advantage. He broke a full nelson with a thrust that sent Sermek reeling back against the plant wall. But Sermek recovered quickly and sprang forward again. Leaping into the air, he lunged at Ator, and with one hand, short-circuited the receiving antenna atop the giant's head. Ator crashed to the ground.

196 .

Sermek had won!

Tom flung open the control-house door and dashed out, Ator's temporary master might have taken over the controls at the relay board and television screen in the plant. Racing past the fallen robot, he slipped through the milling crowd of workers and entered the double-walled enclosure which housed the long relay board. Abruptly Tom stopped in his tracks. Bud was coming down the pa.s.sageway, xveaving from side to side.

"Bud, what-"

"Electric shock," his friend panted, leaning against the wall for support. "I just came to. Knocked me out."

"Take it easy, Bud," Tom said. "Are you all right now?"

"Yes. But listen, Tom," he gasped. "On a hunch, I went to see if anyone was tampering with the relay panel. I saw Robert Turnbull at the controls just as I turned into the corridor! Then the shock hit me and I blacked out."

"Robert Turnbull!" Tom exclaimed. "Are you sure?"

"Positive, Tom!"

"Let's have a look at the relay panel," Tom said quietly.

The boys found a small secondary control board wired into the main panel feed line. A single shunt enabled its operator to disconnect Tom's wiring and subst.i.tute his own, completely by-pa.s.sing the con- THE GIANTS CLASH 197.

trol-house wires. The evidence against Turnbull was overwhelming. Tom immediately ordered a building-by-building search. But the scientist had completely disappeared. Meanwhile, Radnor called a security-police conference to outline a plan of action. With no idea where Turnbull would strike next, every precaution had to be taken to protect the plant.

"We'll need a key man at each vital point," Radnor said. "Hank will watch the entrance gate. Arvid Hanson can guard the robots. I've already alerted the radar technicians to put a double watch on the patrolscopes."

Mr. Swift suggested that he remain in the control house to work the robots if the need arose.

While the men completed their plans, Tom, who had been deep in thought, startled the group by suddenly remarking, "I don't think that I've ever met the real Robert Turnbull. I think that Raymond- not Robert-has been working for us, here, for the past few weeks at least."

"What makes you think that?" Radnor asked in amazement.

"It all begins to tie in, Rad," Tom replied. "For instance, it explains Stan Lee's mysterious failure on that first test run out here and the way our enemies always knew our plans in advance, even after we discovered the recorder in the Flying Lab model."

"I agree, Tom," Mr. Swift said. "Raymond, pa.s.sing successfully as his brother, probably used your stolen relotrol to take over Stan Lee's controls. And I 198 .

think we can a.s.sume he intercepted Hanson's clearance papers. It probably was just another attempt to disrupt plant operations."

"Then what has happened to Robert Turnbull?" Radnor asked.

"Raymond might be holding him a prisoner," Tom replied. "And there aren't many places around here where he could be hiding him. Better check in town first, Rad. Meanwhile, I'll brief Dad on the robot controls."

After the men had left to take their appointed stations, Radnor telephoned the small hotel in town. He gave the clerk a description of Turnbull and asked if such a person was registered there. He was told that no one answering the description had taken a room. Further checking failed to provide a single lead in the small town.

Tom returned from the robot-control house and suggested that Bud and Radnor go with him on a search flight through the surrounding territory. Maps were checked for likely hide-outs in the vicinity. The mesa area with its natural creva.s.ses and rock formations seemed the most logical starting point for the hunt.

With Tom at the controls, the Flying Lab was airborne fifteen minutes after a decision had been reached on the route they would take. Rad sat in the c.o.c.kpit with Tom, while Bud stationed himself in the navigation dome. Soon a familiar view loomed ahead. They were approaching Purple Mesa.

THE GIANTS CLASH 199.

"There's the old 'crows' nest,' " Bud called.

Tom reached for binoculars and scanned the face of the mesa closely. "You may have something there," he said.

The young inventor switched on the jet lifters and slowly guided the Sky Queen alongside Purple Mesa, approaching it from an unfamiliar angle.

"Well, will you look at that!" Bud yelled incredulously.

Directly before them was the entrance to an immense natural cavern, protected by overhanging boulders. The cave seemed to tunnel back from a large outcropping stone lip on which a midget black helicopter rested. Before Tom and his group had time to decide on a course of action, a flock of mechanical crows swarmed out of the cave and swung into formation over the Flying Lab.

One crow broke from the echelon and bore down in a screaming dive toward the mid-section of the huge plane. Its tremendous impact shook the fuselage, and the crow shattered in all directions against the Queen's Tomasite covering.

The rest of the flock attacked simultaneously, crashing into the wings and cabin.

The great ship shivered but held steady. A second flock of mechanical missiles zoomed out of the cave at high speed. In rapid succession they slammed into the ship, battering themselves to pieces. The attack ended as abruptly as it had begun.

"Either they've run out of crows or they decided not to waste any more on us," Tom remarked.

200 .

"I bet they've thrown everything they had at us," Bud said. "Now let's get them!"

Radnor took over the controls and held the plane motionless at the edge of the shelf. Tom and Bud dropped a rope ladder and lowered themselves carefully to the rocky table. Tom cautiously entered the cave, Bud at his heels. The limestone interior was illuminated by incandescent lamps recessed in the cave walls. The boys continued on, following the lights, and soon found themselves in a pa.s.sageway. After a short distance it turned abruptly and Tom and Bud stood before a rack of electronic controls.

"Seems to be a transmitter," Bud whispered. "But part of it looks something like your relotrol."

Tom nodded grimly and signaled to go on. They pa.s.sed the control board and entered a large irregular cavern. About one third of the stone room was filled with a Diesel engine, a generator, and a large fuel-storage tank. On workbenches were various parts used in a.s.sembling the mechanical crows.

" 'Crows' nest' is right!" Bud whispered. "What a layout! But how did they get all this equipment in here?"

"I'd guess they dismantled it and ferried the sections in by helicopter," Tom said. "But where's the crows' owner? Somebody sent out those mechanical birds to attack us!"

"Do you think it's a trap?"

"We'll soon know, Bud. Come on, and be ready for trouble."

THE GIANTS CLASH 201.

Leaving the machine-equipped area, they entered a dead-end room and found themselves face to face with the Turnbull twins!

One stood there, triumphant, with arms crossed and a wild, gloating look in his eyes. The other, haggard and drawn, was chained to the wall of the cave. On a table in front of them was an odd-looking mechanical gadget which Tom eyed with distrust.

For a moment no one moved. Then Tom approached the gaunt prisoner.

"Robert," he said gently, "I'm Tom Swift."

The man looked up at Tom with pleading eyes. "You should never have come here," he gasped.

"What do you mean?"

Robert strained against his bonds. "Tom," he warned frantically, "my brother plans to destroy the atomic energy plant and do away with you and your father."

Raymond's eyes gleamed in the glaring light. "I'll ruin all of them-the Swifts, the physicists too!" His voice rose to a screech. "I'll smash the atom smashers.

Ha! That's pretty good! I'll turn the Citadel back into atoms. Nothing but atoms."

He advanced menacingly toward Tom. "The atomic plant's as good as wrecked, Swift. The damage to the thermopile has already been done. I've seen to that. It will blow up six hours from now!"

Tom, looking sideways at Bud, said calmly, "Maybe there was an outfield error in your calculations, professor!"

202 .

Bud instantly interpreted the phrase as the code for "Grab this guy!" Both boys closed in on Raymond as he reached toward the switch of the machine on the table.

"When this switch is pulled it will blow up the whole cave and end it for all of us!" he screamed.

CHAPTER 25.

ATOR'S TRIUMPH.

AS RAYMOND reached for the switch, Tom and Bud dived at him. The screaming scientist toppled back, missing the fatal switch by inches! A moment later they had overpowered him. Tom found a set of keys and quickly released Robert Turnbull.

Rather than take the chance that the scientist would reach for the switch again, Bud and Tom manacled Raymond with the chains he had used to imprison his brother.

"We don't have much time," Tom warned. "Let's get to the plant, quick!"

They half pushed, half dragged the unwilling Raymond through the caverns until they reached the outer ledge. Bud helped Robert climb the dangling ladder to the Sky Queen. Then, to save time, Tom asked Radnor to lower a steel line which he hooked to Raymond's chains. The scientist was hauled aboard, raging at his captors.

203.

204 .

Quickly Tom ascended the ladder. With Radnor at the controls again, the Flying Lab headed for the Citadel at top speed. Tom and Bud joined the Turn- bulls in the Sky Queen's lounge.

"Raymond," Tom demanded, "how did you sabotage the plant?"

"Oh, it's ingenious!" he cackled. "Oh my, yes, ingenious. Only I could have figured such a way to destroy your precious Citadel!"

Tom's patience was at an end. "What way?" he cried. "By damaging the bank of moderating rods?"

"Too crude, too crude," Raymond gloated. "I have slugged you, Tom Swift.

That's what I have done. I have really slugged-"

Suddenly Raymond gasped and crumpled unconscious to the floor. Bud and Tom removed the manacles and lifted him onto a bunk.

"He'll be out for hours," Robert said. "He's had these spells on and off ever since his mind snapped."

"Then he'll never be able to tell us in time to save the plant!" Bud cried.

"He may have told us something already," mused Tom.

"What do you mean?" Robert asked.

"I'm not sure yet, and we can't take any chances. I'm going to radio ahead to Dad and have the plant evacuated."