"I'm afraid you still don't see entirely. It wasn't the robot."

"Not the robot?"

"A robot could not have sabotaged the ship. It would have been bringing harm to humans and that would have meant breaking the First Law."

The commander frowned as he considered that. "It might not have been aware that it was doing harm."

"Everyone aboard ship, including the humanoid, understands Agrav. The robot would have known it was doing harm. In any case I think we have the identity of the saboteur, or will have in a moment"

"Oh? Who is he, Councilman Starr?"

"Well, consider this for a moment. If a man so sabotages a ship as to insure that it will either blow up or fall into Jupiter, he would be either a madman or a superhumanly dedicated person to stay on board that ship."

"Yes, I suppose so.''

"Since the time we left Io, the air locks have never opened. If they had there would have been slight drops in air pressure, and the ship's barometer indicates no such drops. You see, then, the saboteur must never have gotten on the ship at Io. He's still there, unless he's been taken off."

"How could he be taken off? No ship could get to Io, except this one."

Lucky smiled grimly. "No Earth ship."

The commander's eyes widened. "Surely no Sirian ship, either."

"Are you sure?"

"Yes, I'm sure." The commander frowned. "And for that matter, wait a moment. Everyone reported on board before we left Io. We wouldn't have left without everyone reported present."

"In that case everyone is still on board."

"I would presume so."

"Well," said Lucky, "Panner has ordered all men to stations under emergency conditions. The where-abouts of every man should be fixed during this dry run. Call Panner and ask if anyone is missing."

Commander Donahue turned to the intercom, and signaled Panner.

There was some delay, and then Panner's voice, infinitely tired, answered. "I was about to call, Commander. The run was successful. We can take off. If we're lucky, things will hold till we're back on Jupiter Nine."

The commander said, "Very good. Your work will be properly acknowledged, Panner. Meanwhile, are all men at stations?"

Panner's face on the visiplate above the intercom seemed to harden all at once. "No! By Space, I meant to tell you! We can't locate Summers."

"Red Summers," Bigman cried in sudden excitement. "That murdering cobber. Lucky…"

"One moment, Bigman," Lucky said. "Dr. Panner, you mean Summers isn't in his quarters?"

"He isn't anywhere. Except that it's impossible, I'd say he wasn't on board."

"Thank you." Lucky reached over to break contact "Well, Commander."

Bigman said, "Listen, Lucky. You remember once I told you I met him coming out of the engine room? What was he doing down there?"

"We know now," said Lucky.

"And we know enough to get him," said the commander, white-faced. "We're landing on Io and…"

"Wait," said Lucky, "first things first. There is something more important even than a traitor."

"What?"

"The matter of the robot."

"That can wait."

"Perhaps not. Commander, you said that all men reported on board the Jovian Moon before we left lo. If so, the report was obviously a false one."

"Well?"

"I think we ought to try to find the source of the false report. A robot can't sabotage a ship, but if a man has sabotaged the ship without the robot's knowledge, it would be very simple for the robot to help that man remain off the ship if its help is requested."

"You mean whoever is responsible for the false report that Summers was on board ship is the robot?"

Lucky paused. He tried not to allow himself to grow too hopeful or feel too triumphant, and yet the argu-men seemed perfect.

He said, "It seems so."

Commander Donahue said, "Major Levinson, then." His eyes darkened. "And yet I find that impossible to believe."

"Find what impossible to believe?" Lucky asked.

"That he is a robot. He's the man who took the report. He keeps our records. I know him well and I swear that he can't be a robot."

"We'll question him, Commander. And one thing-" Lucky's expression was somber. "Don't accuse him of being a robot; don't ask him if he's one or even imply that he might be one. Do nothing to make him feel he's under suspicion."

The commander looked astonished. "Why not?"

"The Sirians have a way of protecting their robots. Open suspicion may trigger some explosive device within the major if he is indeed a robot."

The commander exhaled explosively. "Space!"

Major Levinson showed the signs of strain that were universal among the men aboard the Jovian Moon, but he stood at brisk military attention. "Yes, sir."

The commander said cautiously, "Councilman Starr has a few questions to ask."

Major Levinson shifted to face Lucky. He was quite tall, topping even Lucky's inches, with fair hair, blue eyes, and a narrow face.

Lucky said, "All men were reported on board the Jovian Moon at the tune of take-off from Io, and you prepared that report. Isthat right, major?"

"Yes, sir."

"Did you see each man individually?"

"No, sir. I used the intercom. Each man answered at take-off station or in his cabin."

"Each man? Did you hear each man's voice? Each individual voice?"

Major Levinson looked astonished. "I suppose so. That's not the sort of thing one remembers, really."

"Nevertheless it's quite important and I'm asking you to remember."

The major frowned and bent his head. "Well, now wait. Come to think of it, Norrich answered for Summers because Summers was hi the bathroom." Then, with a sudden spark of excitement, he added, "Hold on, they're looking for Summers right now."

Lucky held up a palm. "Never mind that, Major. Would you get Norrich and send him up?"

Norrich came in on Major Levinson's arm. He looked bewildered. He said, "Commander, no one seems to be able to find Red Summers. What's hap-pened to him?"

Lucky forestalled the commander's answer. He said, "We're trying to find out. Did you report Summers present when Major Levinson checked those aboard before we left Io?"

The blind engineer reddened. He said tightly, "Yes."

"The major says you said Summers was in the bathroom. Was he?"

"Well… No, he wasn't, Councilman. He had gotten off ship for a moment to pick up some item of equipment he had left behind. He didn't want the commander chewing him out-pardon me, sir-for carelessness, and he asked me to cover for him. He said he would be back well before take-off."

"Was he?"

"I… I thought… I had the impression he was. Mutt barked, I think, and I was sure Summers was coming back, but there isn't anything for me to do at take-off, so I was turning in for a nap and I guess I just didn't give the matter too much thought at the moment. Then there was the mess in the engine room almost right away, and after that there was no time to think of anything."

Panner's voice came over the central intercom with sudden loudness. "Warning to all men. We are taking off. Everyone to stations."

The Jovian Moon was in space again, lifting itself against Jupiter's gravity with powerful surges. It was expending energy at a rate that would have bankrupted five ordinary vessels and only the fault tremor in the sound of the hyperatomics remained to show that the ship's mechanism depended, in part, on makeshift devices.

Panner gloomily pondered on the poor showing the ship would now make energy-wise. He said, "As is, I'll get back with only seventy per cent of original energy, when it could have been eighty-five or ninety.

If we land on lo and make another take-off, we'll get back with only fifty. And I don't know if we can stand another take-off."