CHAPTER VI
THE CAISSON CLUE
"Captain Smith" had leaped to his feet, quivering with anger. But it wastoo late. His cellmate, by answering to the name of "Mirov," had givenaway their nationality!
Tom and Ames exchanged grins of triumph.
"No doubt you recall what happened to Streffan Mirov," Tom went on,pressing his advantage. "Or should I say the _late_ Streffan Mirov? Ourlast report was that he had been tried and condemned by your owngovernment. Perhaps you can give us news of his fate?"
The wavy-haired prisoner's eyes blazed with hate. "Grin while you can,Tom Swift! Because of you, my brother Streffan is now serving a longprison sentence! But I, Dimitri Mirov, will get revenge!"
"You blame Tom Swift because your brother botched his job of claimingthe satellite Nestria by force and fraud?" Ames taunted.
"Our space friends moved that asteroid into orbit around the earth," Tomadded. "We claimed it by right of first landing. Even your own leaderscouldn't agree to Streffan's crazy scheme to destroy everything."
Dimitri Mirov lost all control and burst into a volley of gutturalBrungarian abuse.
"I warn you, Swift!" he choked. "Jailing us will not make you safe--oryour projects, either!"
A blow to the head from "Captain Smith" sent Mirov reeling back againstthe wall. "Fool! Maybe that will quiet you!" the pilot snappedviciously. "You have said too much already!"
"Let's go, Tom," said Ames. "We've learned the information we came for."
The prisoners could only glare in baffled rage through the cell bars asTom and the security chief turned their backs and walked away.
"Nice going, Tom," Ames murmured. "Your hunch certainly paid off." ChiefSlater added his congratulations when he heard how Tom had trapped Mirovinto disclosing his identity.
Both Tom and Ames were grave as they drove back to the plant. Neithertook Mirov's threats lightly.
Tom pondered another angle. Were the Brungarian rebels perhapsresponsible for the attempted theft of the Jupiter-circling missile?
Ames was inclined to think so. "Moreover," he forecast, "it's a cinchthey haven't thrown their last punch. I'll pass the word to the FBI andCentral Intelligence."
After lunch Tom flew to Fearing Island with Bud, eager to tackle theirinterrupted job of rooting the space plants into the undersea silt beds.Zimby Cox, a sandy-haired, freckle-faced jetmariner, volunteered topilot a motor launch for them.
They sped across the water, then dropped anchor at the farm site. Tomand Bud donned their hydrolung gear and went over the side, eachclutching containers of the space plants.
Reaching bottom, they glided about in the shadowy green water, embeddingthe plants at far-spaced intervals. The Tomasite-producing plants hadbeen almost completely devoured. A few fish were darting about, but theyswam off quickly at the boys' approach. To Tom's delight, they showed nosign of returning.
"Looks as if our keep-off signs are working," Tom said with a pleasedchuckle when the boys finally surfaced and climbed back aboard the boat.
Bud nodded. "Smart idea, all right." Then he scowled thoughtfully. "Butif you ask me, skipper, fishes aren't the only thieves you'll have toguard against."
"Meaning?"
"Mirov's pals," Bud replied. "If it's the space plants they were afterwhen they pulled that aerial hijack attempt, they could take them easilyfrom these silt beds."
Tom sobered. "You have a point there. I'd better have an audio screenset up around this whole area. That'll act as a burglar alarm--and helpdiscourage the fish, too."
Twenty minutes later the boys were winging back to the mainland. WhenTom reached his office, he called in Gib Brownell, an Enterprisesengineer.
"Got a job for me, skipper?"
Tom handed him a hastily scribbled diagram of the audio-screen setup."One of those hurry-up deals, Gib," he said with an apologetic grin. Tomexplained his plan. "We'll use transmitter buoys, monitored by an alarmsystem at base headquarters on Fearing."
Brownell studied the diagram and nodded. "Right. We can have it set upin twenty-four hours."
As Brownell left the office, the telephone jangled. Tom reached for it.
"Admiral Walter calling." His voice was tense. "Important news, Tom. Oneof our subs has picked up a clue that someone has been operating in themissile search area."
"What sort of clue, sir?" Tom asked.
"A compressed-air caisson for underwater work. It had been driven intothe silt and then abandoned." Admiral Walter added that photographs anda section of the caisson were being flown to the Naval ResearchLaboratory for careful study. "I'll have a full report transmitted toyou by video as soon as it reaches my desk."
Tom thanked the admiral and hung up, feeling more uneasy than ever. Thereport came through the following morning. Tom absorbed the contents,then gave a low whistle.
"Trouble?" asked Bud, who had just dropped into the office with someflight-test data on a new Swift superjet.
"Our old enemies again." Tom shoved the papers across his desk.
The report stated that both the design and manufacturing techniques usedin making the caisson indicated that it was of Brungarian origin. Aspectrographic analysis of the steels confirmed the theory. Theirmetallurgical content agreed with known Brungarian steel formulas.
"The sneaky rats!" Bud cried out. "Well, at least we know now whosabotaged our missile recovery."
As Tom paced about the office, Bud added, "What do you suppose they wereusing the caisson for?"
"Probably as a base for some heavy, rotating search equipment," theyoung inventor surmised.
"But why ditch it?"
Tom shrugged. "An optimistic guess is that they spotted our Navy searchforce and pulled out quickly, fearing a surprise attack."
"What's a pessimistic explanation?" Bud asked.
"Mission completed," Tom said grimly. "No need for them to stick aroundif they'd already snagged the missile."
Bud scowled at the thought. "Oh, no! That mustn't be true!"
Tom plopped down at his desk, frowning. "Bud, I've been itching to getto work on a non-detectable sub, like the one that attacked us. Butmaybe it would be smarter to get a line on Mirov's pals first."
"You mean down in the South Atlantic?"
Tom nodded. "I'd sure like to know if they found that missile."
"You and I both, pal!" Bud agreed. "Hey! We could use the electronichydrolungs for scouting around!" he added eagerly.
"I intend to," Tom said. "But we'll need speed to cover the area. Sofirst I want to add an ion drive to our equipment."
"Ion drive? For underwater?" Bud, who was familiar with ion propulsionfor spaceships, wrinkled his brow in a puzzled frown.
"A goofy idea just occurred to me, but I think it may work out," Tomreplied. He seized a pencil and began explaining what he had in mind.
The drive unit would take water into itself, separate the ionizedmolecules, and expose them to an electric field. Thus a stream of waterwould be forced out. This procedure, in turn, would set up a siphoningaction through a central tube--in effect, creating a small but powerfulwater-jet motor.
"We'll be human submarines!" Bud exclaimed.
By the time Bud left the laboratory half an hour later, Tom had alreadyplunged into work on his newest invention. The idea was simple enough initself, Tom felt. The main problem would be the design job--laying out acompact, lightweight unit which a swimmer could easily carry on hisback.
Fascinated, the young inventor worked late into the evening, stoppingonly in response to a telephone plea from Mrs. Swift. By midmorning thenext day, Tom had assembled a pilot model of his ion-drive jet. Inappearance, it was a slender metal cylinder, two feet long, with aninner concentric tube projecting at each end.
Tom had ordered a tank set up in his laboratory to test the unit. Thetank was filled chest-deep with water, and the ion drive was mounted ona unitrack running the length of it. Tom set up his control boardalongside, with the main power switch within easy reach. The drive unitwas
connected to the board by a suspended cable.
"Boy, this'll be like playing with a speedboat in a bathtub!" Tomthought with a chuckle as he changed into swim trunks.
He climbed into the tank and slid the drive unit to one end of itstrack. Then Tom metered out power slowly. With a gentle _whoosh_, theion-drive unit whizzed along the unitrack to the other end of the tank.
"Not bad," Tom muttered, a pleased grin on his face. "Now I'll rev it upa little."
He slid the drive unit back to starting position, then opened the switchwider. He had just started across the tank himself when suddenly hebecame powerless to move.
Tom was pinned helplessly against the wall of the tank by the powerfulwater-jet exhaust! And the control switch was beyond his reach!