Lucky said, "I thought of that, too, Bigman, and that's one reason I brought Panner down here. He's obviously acquainted with the engines. I've watched him inspect everything and he couldn't have done it with such assurance if he weren't an expert on the workings."
"Does that suit you, Martian?" Panner demanded with suppressed anger.
Bigman put his needle-gun away, and without a further word Panner scrambled up the ladder.
They stopped off at the next level, working through it a second time.
Panner said, "All right, that leaves ten men: two army officers, four engineers, four workmen. What dp you propose to do? X-ray each of them separately? Something like that?"
Lucky shook his head. "That's too risky. Apparently the Sirians have been known to use a cute little trick to protect themselves. They've been known to use robots to carry messages or to perform tasks which the individual giving the orders wanted to be kept secret. Now obviously a robot can't keep a secret if a human being asks him, in the proper fashion, to reveal it. What the Sirians do, then, is to install an explosive device in the robot which is triggered by any attempt to force the robot to give away the secret."
"You mean if you put an X-ray on the robot, it will explode?"
"There's a very good chance that it would. Its greatest secret is its identity, and it may be triggered for every attempt to discover that identity that the Sirians could think of." Lucky added regretfully, "They hadn't counted on a V-frog; there was no trigger against that. They had to order the robot to kill the V-frog directly. Or that might have been preferable anyway, since it managed to keep the robot alive undetected."
"Wouldn't the robot be harming humans nearby if it exploded? Wouldn't it be breaking First Law?" asked Panner with a trace of sarcasm.
"It wouldn't. It would have no control over the explosion. The triggering would be the result of the sound of a certain question or the sight of a certain action, not the result of anything the robot itself would do."
They crawled up to still another level.
"Then what do you expect to do, Councilman?" demanded Panner.
"I don't know," Lucky said frankly. "The robot must be made to give itself away somehow. The Three Laws, however modified and fancified, must apply. It's only a question of being sufficiently acquainted with robotics to know how to take advantage of those Laws. If I knew how to force the robot into some action that would show it to be non-human without activating any explosive device with which it might be equipped; if I could manipulate the Three Laws so as to force one to conflict with another sufficiently strongly to paralyze the creature completely; if I-"
Panner broke in impatiently, "Well, if you expect help from me, Councilman, it's no use. I've told you already I know nothing of robotics." He whirled suddenly. "What's that?"
Bigman looked about, too. "I didn't hear anything."
Wordlessly Panner squeezed past them, dwarfed by the bending metal tube on either side.
He had gone almost as far as he could, the other two following, when he muttered, "Someone might have squeezed in among the rectifiers. Let me pass again."
Lucky stared, frowning, into what was almost a forest of twisting cables that enclosed them in a complete dead end.
Lucky said, "It seems clear to me."
"We can test it for sure," Panner said tightly. He had opened a panel in the wall nearby and now he reached in cautiously, looking over his shoulder.
"Don't move," he said.
Bigman said testily, "Nothing's happened. There's nothing there."
Panner relaxed. "I know it. I asked you not to move because I didn't want to slice an arm off when I established the force field."
"What force field?"
"I've shorted a force field right across the corridor. You can't move out of there any more than you could if you were encased in solid steel three feet thick."
Bigman yelled, "Sands of Mars, Lucky, he is the robot!" His hand lunged.
Panner cried at once, "Don't try the needle-gun. Kill me and how do you ever get out?" He stared at them, dark eyes sparking, his broad shoulders hunched. "Remember, energy can get through a force field but matter can't, not even air molecules. You're airtight in there. Kill me and you'll suffocate long before anyone happens to come across you down here."
"I said he was the robot," said Bigman in raging despair.
Panner laughed shortly, "You're wrong. I'm not a robot. But if there is one, I know who it is."
11. Down the Line of Moons
"Who?" Bigman demanded at once.
But it was Lucky who answered. "Obviously he thinks it's one of us."
"Thanks!" said Panner. "How would you explain it? You mentioned stowaways; you talked about people forcing their way on board the Jovian Moon. Talk about nerve! Aren't there two people who did force their way on board? Didn't I witness the process? You two!"
"True enough," said Lucky.
"And you brought me down here so you could investigate every inch of the ship's workings. You tried to keep me busy with stories about robots hoping I wouldn't notice that you two were going over the whole ship with a microscope."
Bigman said, "We have a right to do it. This is Lucky Starr!"
"He says he's Lucky Starr. If he's a member of the Council of Science, he can prove it and he knows how. If I had any brains, I'd have demanded identification before taking you down."
"It's not too late now," Lucky said calmly. "Can you see clearly from that distance?" He held up one arm, palm forward, and peeled the sleeve back.
"I'm not coming any closer," Panner said angrily.
Lucky said nothing to that. He let his wrist tell the story. The skin along the inner surface of his wrist seemed merely exposed skin, but years before it had been treated hormonally in a most complicated fashion. Responding to nothing more than a disciplined effort of Lucky's will, an oval spot on the wrist darkened and slowly turned black. Within it, little yellow specks formed in the familiar patterns of the Big Dipper and of Orion.
Panner gasped as though the breath had been forcibly knocked out of his lungs. Few human beings had the occasion to see this sign of the Council, but all above the age of childhood knew it for what it was- the final and unforgeable identification insigne of the councilman of science.
Panner was left with no choice. Silently, reluctantly, he released the force field and stepped back.
Bigman came out, raging, "I ought to bend in your skull, you lopsided-"
Lucky pulled him back. "Forget it, Bigman. The man had as much right to suspect us as we had to suspect him. Settle down."
Panner shrugged. "It seemed logical."
"I admit it did. I think we can trust each other now."
"You, maybe," the chief engineer said pointedly. "You're identified. What about this little loudmouth with you? Who identifies him?"
Bigman squawked incoherently and Lucky stepped in between the two. "I identify him and take full responsibility for him… Now I propose that we get back to passenger quarters before a search is organized for us. Everything that went on down here is, of course, strictly confidential."
Then, as though nothing had happened, they resumed the climb upward.
The room assigned to them contained a two-decker bed and a washstand out of which a small trickle of water could be urged. Nothing more. Even the cramped and Spartan quarters on board the Shooting Starr were luxury to this.
Bigman sat cross-legged on the upper bed, while Lucky sponged his neck and shoulders. They talked in whispers, conscious of the listening ears that might be present on the other side of the walls.
Bigman said, "Look, Lucky, suppose I go up to each person on board ship; I mean, each of the ten we don't know about? Suppose I deliberately pick a fight with each one, call them a few names, things like that? Wouldn't it turn out that the guy who doesn't take a punch at me is the robot?"