"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.

"You're sure?" Domgraf-Schwach asked. "You really know which is the negative control sample?"

"I know." Fisher noted his findings on the punch sheet and moved away.

"I'm next," Tate said, impatiently pushing up. "Let's get this over with."

One by one, the men examined the two samples, recorded their findings, and then moved off to stand waiting uneasily.

"All right," Portbane said finally. "I'm the last one." He peered down briefly, scribbled his results, then pushed the equipment away. "Give me the readings," he told the workmen by the scanner.

A moment later, the findings were flashed up for everyone to see.

Fisher A

Tate A

O'Keefe B

Horstokowski B

Silberman B

Daniels B

Portbane A

Domgraf-Schwach B

Lanoir A

"I'll be damned," Silberman said softly. "As simple as that. We're paranoids."

"You cluck!" Tate shouted at Horstokowski. "It was A, not B! How the hell could you get it wrong?"

"B was as bright as a searchlight!" Domgraf-Schwach answered furiously. "A was completely colorless!"

O'Keefe pushed forward. "Which was it, Portbane? Which was the positive sample?"

"I don't know," Portbane confessed. "How could any of us be sure?"

The buzzer on Domgraf-Schwach's desk clicked and he snapped on the vidscreen.

The face of a soldier-operator appeared. "The attack's over, sir. We drove them away."

Domgraf-Schwach smiled ironically. "Catch any of them?"

"No, sir. They slipped back into the bog. I think we hit a couple, though. We'll go out tomorrow and try to find the corpses."

"You think you'll find them?"

"Well, the bog usually swallows them up. But maybe this time --"

"All right," Domgraf-Schwach interrupted. "If this turns out to be an exception, let me know." He broke the circuit.

"Now what?" Daniels inquired icily.

"There's no point in continuing work on the ship," O'Keefe said. "Why waste our time bombing empty bogs?"

"I suggest we keep working on the ship," Tate contradicted.

"Why?" O'Keefe asked.

"So we can head for Fomalhaut and give ourselves up to the hospital station."

Silberman stared at him incredulously. "Turn ourselves in? Why not stay here? We're not harming anybody."

"No, not yet. It's the future I'm thinking of, centuries from now."

"We'll be dead."

"Those of us in this room, sure, but what about our descendants?"

"He's right," Lanoir conceded. "Eventually our descendants will fill this whole solar system. Sooner or later, our ships might spread over the Galaxy." He tried to smile, but his muscles would not respond. "The tapes point out how tenacious paranoids are. They cling fanatically to their fixed beliefs. If our descendants expand into Terran regions, there'll be a fight and we might win because we're more one-track. We would never deviate."

"Fanatics," Daniels whispered.

"We'll have to keep this information from the rest of the camp," O'Keefe said.

"Absolutely," Fisher agreed. "We'll have to keep them thinking the ship is for H-bomb attacks. Otherwise, we'll have one hell of a situation on our hands."

They began moving numbly toward the sealed door.

"Wait a minute," Domgraf-Schwach said urgently. "The two workmen." He started back, while some of them went out into the corridor, the rest back toward their seats.

And then it happened.

Silberman fired first. Fisher screamed as half of him vanished in swirling particles of radioactive ash. Silberman dropped to one knee and fired up at Tate. Tate leaned back and brought out his own B-pistol. Daniels stepped from the path of Lanoir's beam. It missed him and struck the first row of seats.

Lanoir calmly crept along the wall through the billowing clouds of smoke. A figure loomed ahead; he raised his gun and fired. The figure fell to one side and fired back. Lanoir staggered and collapsed like a deflated balloon and Silberman hurried on.

At his desk, Domgraf-Schwach was groping wildly for his escape button. His fingers touched it, but as he depressed the stud, a blast from Portbane's pistol removed the top of his head. The lifeless corpse stood momentarily, then was whisked to "safety" by the intricate apparatus beneath the desk.

"This way!" Portbane shouted, above the sizzle of the B-blasts. "Come on, Tate!"

Various beams were turned in his direction. Half the chamber burst apart and thundered down, disintegrating into rubble and flaming debris. He and Tate scrambled for one of the emergency exits. Behind them, the others hurried, firing savagely.