'Then we were prisoners," Tate said, dazed.

"Whose?" Fisher asked baffledly.

"The Terrans!" Lanoir said.

"I don't get it," Fisher muttered vaguely. "We planned the whole flight—didn't we? We broke out of Ganymede and got away."

"Get the tapes going," Portbane said to Lanoir. "Let's see what's in them."

Daniels snapped the vidtape scanner off and raised the light.

"Well," he said, "you saw for yourselves this was a hospital ship. It carried no crew. It was directed from a central guide-beam at Jupiter. The beam carried it from the Sol System here, where, because of a mechanical error, a meteor penetrated the protection screen and the ship crashed."

"And if it hadn't crashed?" Domgraf-Schwach asked faintly.

'Then we would have been taken to the main hospital at Fomalhaut IV."

"Play the last tape again," Tate urged.

The wall-speaker spluttered and then said smoothly: "The distinction between paranoids and paranoiac syndromes in other psychotic personality disorders must be borne in mind when dealing with these patients. The paranoid retains his general personality structure unimpaired. Outside of the region of his complex, he is logical, rational, even brilliant. He can be talked to—he can discuss himself—he is aware of his surroundings.

"The paranoid differs from other psychotics in that he remains actively oriented to the outside world. He differs from so-called normal personality types in that he has a set of fixed ideas, false postulates from which he has relentlessly constructed an elaborate system of beliefs, logical and consistent with these false postulates."

Shakily, Daniels interrupted the tape. "These tapes were for the hospital authorities on Fomalhaut IV. Locked in a supply closet in the control cabin. The control cabin itself was sealed off from the rest of the ship. None of us was able to enter it."

"The paranoid is totally rigid," the calm voice of the Terran doctor continued. "His fixed ideas cannot be shaken. They dominate his life. He logically weaves all events, all persons, all chance remarks and happenings, into his system. He is convinced the world is plotting against him—that he is a person of unusual importance and ability against whom endless machinations are directed. To thwart these plots, the paranoid goes to infinite lengths to protect himself. He repeatedly vidtapes the authorities, constantly moves from place to place and, in the dangerous final phases, may even become—"

Silberman snapped it off savagely and the chamber was silent. The nine leaders of the camp sat unmoving in their places.

"We're a bunch of nuts," Tate said finally. "A shipload of psychos who got wrecked by a chance meteor."

"Don't kid yourself," Horstokowski snapped. "There wasn't anything chance about that meteor."

Fisher giggled hysterically. "More paranoid talk. Good God, all these attacks—hallucinations—all in our minds!"

Lanoir poked vaguely at the piles of tape. "What are we to believe? Are there any attackers?"

"We've been defending ourselves against them for five years!" Portbane retorted. "Isn't that proof enough?"

"Have you ever seen them?" Fisher asked slyly.

"We're up against the best agents in the Galaxy. Terran shock troops and military spies, carefully trained in subversion and sabotage. They're too clever to show themselves."

"They wrecked the bridge-system," O'Keefe said. "It's true we didn't see them, but the bridge is sure as hell in ruins."

"Maybe it was badly built," Fisher pointed out. "Maybe it just collapsed."

"Things don't 'just collapse'! There's a reason for all these things that have been happening."

"Like what?" Tate demanded.

"Weekly poison gas attacks," Portbane said. "Metallic wastes in the water supply, to name only two."

"And bacteriological crystals," Daniels added.

"Maybe none of these things exist," Lanoir argued. "But how are we to prove it? If we're all insane, how would we know?"

"There are over a hundred of us," Domgraf-Schwach said. "We've all experienced these attacks. Isn't that proof enough?"

"A myth can be picked up by a whole society, believed and taught to the next generation. Gods, fairies, witches— believing a thing doesn't make it true. For centuries, Terrans believed the Earth was flat."

"If all foot-rulers grow to thirteen inches," Fisher asked, "how would anybody know? One of them would have to stay twelve inches long, a nonvariable, a constant. We're a bunch of inaccurate rulers, each thirteen inches long. We need one nonparanoid for comparison."

"Or maybe this is all part of their strategy," Silberman said. "Maybe they rigged up that control cabin and planted those tapes there."

"This ought to be no different from trying to test any belief," Portbane explained. "What's the characteristic of a scientific test?"

"It can be duplicated," Fisher said promptly. "Look, we're going around in circles. We're trying to measure ourselves. You can't take your ruler, either twelve inches or thirteen inches long, and ask it to measure itself. No instrument can test its own accuracy."

"Wrong," Portbane answered calmly. "I can put together a valid, objective test."

"There's no such test!" Tate shouted excitedly.

"There sure as hell is. And inside of a week, I'll have it set up."

"Gas!" the soldier shouted. On all sides, sirens wailed into life. Women and children scrambled for their masks. Heavy-duty cannon rumbled up from subsurface chambers and took up positions. Along the perimeter of the bog, the fusing bugs were searing away a ribbon of muck. Searchlights played out into the fern-thick darkness.

Portbane snapped off the cock of the steel tank and signaled the workmen. The tank was rolled quickly away from the sea of mud and seared weeds.

"All right," Portbane gasped. "Get it below."

He emerged in the subsurface chamber as the cylinder was being rolled into position.

"That cylinder," Portbane said, "should contain hydrocyanic vapor. It's a sampling made at the site of the attack."

"This is useless," Fisher complained. "They're attacking and here we stand!"

Portbane signaled the workmen and they began laying out the test apparatus. "There will be two samples, precipitates of different vapors, each clearly marked and labeled A and B. One comes from the cylinder filled at the scene of the attack. The other is condensed from air taken out of this room."

"Suppose we describe both as negative?" Silberman asked worriedly. "Won't that throw your test off?"

"Then we'll take more tests. After a couple of months, if we still haven't got anything but negative findings, then the attack hypothesis is destroyed."

"We may see both as positive," Tate said, perplexed.

"In that case, we're dead right now. If we see both samples as positive, I think the case for the paranoid hypothesis has been proved."

After a moment, Domgraf-Schwach reluctantly agreed. "One is the control. If we maintain that it isn't possible to get a control sample that is free of hydrocyanic acid..."

"Pretty damn slick," O'Keefe admitted. "You start from the one known factor—our own existence. We can't very well doubt that."

"Here are all the choices," Portbane said. "Both positive means we're psychotic. Both negative means either the attack was a false alarm or there are no attackers. One positive and one negative would indicate there are real attackers, that we're fully sane and rational." He glanced around at the camp leads. "But we'll all have to agree which sample is which."

"Our reactions will be recorded secretly?" Tate asked.

"Tabulated and punched by the mechanical eye. Tallied by machinery. Each of us will make an individual discrimination."

After a pause, Fisher said, "I'll try it." He came forward, leaned over the colorimeter and studied the two samples intently. He alternated them for a time and then firmly grabbed the check-stylus.