It was Lucky who broke the deadly silence that followed, in sharp, incisive tones. "No man is dead while he has a mind capable of thought. Who can handle this ship's computer most rapidly?"

Commander Donahue said, "Major Brant. He's the regular trajectory man."

"Is he up in the control room?"

"Yes."

"Let's get to him. I want the detailed Planetary Ephemerae ... Panner, you stay here with the men and get to work cannibalizing and improvising."

"What good will it-?" Panner began.

Lucky cut in at once. "Perhaps no good at all. If so, we'll hit Jupiter and you'll die after having wasted a few hours of labor. Now I've given you an order. Get to work!"

"But..." Commander Donahue seemed stuck after that one word.

Lucky said, "As councilman of science, I'm assuming command of this vessel. If you wish to dispute that, I'll have Bigman lock you in your cabin and you can argue it out at the court-martial proceedings, assuming we survive."

Lucky turned away and moved quickly up the central shaft. Bigman motioned Commander Donahue up with a quick jerk of his thumb and followed last.

Panner looked after them scowling, turned savagely to the engineers, and said, "All right, you bunch of corpses. No use waiting for it with our fingers in our mouths. Hop to it."

Lucky strode into the control room.

The officer at the controls said, "What's wrong down there?" His lips were white.

"You're Major Brant," said Lucky, "We haven't been formally introduced, but never mind that. I'm Councilman David Starr, and you're taking orders from me. Get at that computer and do what you're told with all the speed you have."

Lucky had the Planetary Ephemerae before him. Like all great reference works, it was in book form rather than film. The turning of pages, after all, made for the more rapid location of a specific piece of information, than did the long-drawn-out unwinding of film from end to end.

He turned the pages now with practiced hand, searching among the rows and columns of numbers that located the position of every chunk of matter in the solar system over ten miles in diameter (and some under) at certain standard tunes, together with their planes of revolution and velocity of motion.

Lucky said, "Take the following co-ordinates as I call them out, together with the line of motion, and calculate the characteristics of the orbit and the position of the point at this moment and for succeeding moments for the space of forty-eight hours."

The major's fingers flew as figures were converted by the special punch machine into a coded tape which was fed into the computer.

Even while that was taking place, Lucky said, "Calculate from our present position and velocity our orbit with respect to Jupiter and the point of intersection with the object whose orbit you have just calculated."

Again the major worked.

The computer spat out its results in coded tape that wound on to a spool and dictated the tapping of a typewriter that spelled out the results in figures.

Lucky said, "At the point of intersection, what is time discrepancy between our ship and the object?"

Again the major worked. He said, "We miss it by four hours, twenty-one minutes, and forty-four seconds."

"Calculate how the velocity of the ship must be altered in order to hit the point squarely. Use one hour from now as the starting time."

Commander Donahue broke in. "We can't do anything this close to Jupiter, Councilman. The emergency power won't break us away. Don't you understand that?"

"I'm not asking the major to break us away, Commander. I'm asking him to accelerate the ship toward Jupiter, for whatever our reserve power is worth."

The commander rocked back on his heels. "Toward Jupiter?"

The computer was making the calculation and the results were coming in. Lucky said, "Can you accelerate by that much on the power available?"

Major Brant said shakily, "I think so."

"Then do it."

Commander Donahue said again, "Toward Jupiter?"

"Yes. Exactly. Io isn't the innermost of Jupiter's satellites. Amalthea is closer, Jupiter Five. If we can intersect its orbit properly, we can land on it. If we miss it, well, then, we will have hurried death by two hours."

Bigman felt a surge of sudden hope. He could never entirely despair while Lucky was in action, but until that moment he had not seen what it was that Lucky intended doing. He remembered now his earlier conversation with Lucky on the subject. The satellites were numbered in order of discovery. Amalthea was a small satellite, just a hundred miles in diameter, and it was discovered only after the four major satellites were known. So, though the closest to Jupiter, it was Jupiter Five. Somehow one tended to forget that. Because Io was called Jupiter One, there was always the tendency to think there was nothing between it and the planet itself.

And one hour later the Jovian Moon began a carefully plotted acceleration toward Jupiter, hastening toward the death trap.

They no longer centered the visiplate on any part of Jupiter. Though the latter swelled hourly, the center of sight remained on a portion of the star field a considerable distance from Jupiter's rim. The star field was under maximum magnification. At that point should be Jupiter Five, streaking for its rendezvous with a ship which was hurtling and straining down, down toward Jupiter. Either the ship would be caught by the speck of rock and saved, or it would miss and be lost forever.

"There it is," said Bigman in excitement. "That star shows a visible disk."

"Calculate observed position and motion," ordered Lucky, "and check with the computed orbit."

This was done.

"Any correction?" Lucky asked.

''We'll have to slow down by-"

''Never mind the figures. Do it!"

Jupiter Five circled Jupiter in twelve hours, moving in its orbit at a speed of nearly three thousand miles an hour. This was one and a half times as rapid as Io's motion and its gravitational field was only one twentieth that of Io. For both reasons, it made the harder target.

Major Brant's fists trembled on the controls as the all-important side thrusts bent the Jovian Moon's orbit ever so slightly to meet the onrushing Jupiter Five, slip behind it and round, matching speeds for just those vital moments that would enable the satellite's gravity to establish the ship in an orbit about itself.

Jupiter Five was a large, brilliant object now. If it stayed so, good. If it began to grow smaller, they had missed.

Major Brant whispered, "We've made it," and bis head fell forward into his shaking palms as he released the controls.

Even Lucky closed his eyes momentarily in a land of weary relief.

In one way the situation on Jupiter Five was far different from what it had been on Io. There, all the crew had been sight-seers; the consideration of the heavens had taken precedence over the leisurely preparations in the valley.

Here on Jupiter Five, however, no one emerged from the Jovian Moon. What there was to see, no one saw.

The men stayed aboard the ship and worked on the repair of the engines. Nothing else mattered. If they failed, the landing on Jupiter Five could only postpone doom and stretch it out into greater agony.

No normal ship could land on Jupiter Five to rescue them, and no other Agrav ship existed or would exist for a year at least. If they failed, there would be time enough to watch Jupiter and the vision of the skies while they waited for death.

Yet under less urgent conditions the vision would have been worth watching. It was Io all over again with everything doubled and tripled.

From the point at which the Jovian Moon landed, Jupiter's lower rim seemed to sweep the flat, powdery horizon. The giant looked so close in the airlessness that a watcher would have imagined he could reach out his hand and bury it in that circle of light.

From the horizon Jupiter stretched upward, halfway to zenith. At the moment the Jovian Moon landed, Jupiter was almost full, and within the unbearable circle of brilliant stripes and colors nearly ten thousand full moons Earth variety, could have been placed. Almost one sixteenth of the entire vault of the sky was covered by Jupiter.

And because Jupiter Five circled Jupiter in twelve hours, the visible moons-there were four here rather than three as on Io, since Io itself was now a moon - moved three times as fast as they did on Io. So did all the stars and everything else in the sky, except for frozen Jupiter, which one side of the satellite eternally faced and which therefore never moved.

In five hours the sun would rise and it would be exactly the same in appearance as on Io; it would be the one thing that hadn't changed. But it would race toward a four-times-as-large Jupiter at three times the speed and make an eclipse a hundred times as terri-fyingly beautiful.

But no one saw it. It took place twice while the Jovian Moon stayed and no one saw it No one had the time. No one had the heart

Panner finally sat down and stared out of bleary eyes. The flesh around them was red and puffy. His voice was a hoarse whisper.

"All right. Everyone to your normal stations. We'll have a dry run." He hadn't slept in forty hours. The others had worked in shifts, but Panner had stopped neither to eat nor to sleep.

Bigman, who had confined himself to unskilled labor, to fetching and carrying, to reading dials under direction and holding levers according to instruction, had no place in a dry run, no station, no duties. So he wandered somberly about the ship in search of Lucky and found him in the control room with Commander Donahue.

Lucky had his shirt off and was wiping his shoulders, forearms, and face on a large plastofluff towel.

As soon as he saw Bigman, he said briskly, "The ship will be moving, Bigman. We'll be taking off soon."

Bigman's eyes raised. "We're only doing a dry run, Lucky."

"It will work. That Jim Panner worked miracles."

Commander Donahue said stiffly, "Councilman Starr, you have saved my ship."

"No, no. Panner deserves the credit. I think half the engine is being held together with copper wire and mucilage, but it will work."

"You know what I mean, Councilman. You drove us on to Jupiter Five when the rest of us were ready to give up and panic. You saved my ship, and I will report that fact fully when I stand court-martial on Earth for having failed to co-operate with you on Jupiter Nine."

Lucky flushed in embarrassment. "I can't allow that, Commander. It is important that councilmen avoid publicity. As far as the official record is concerned, you will have remained in command at all times. There will be no mention of any actions of mine."

"Impossible. I couldn't allow myself to be praised for what you have done."

"You will have to. It's an order. And let's have no talk of court-martials."

Commander Donahue drew himself up with a kind of pride. "I deserve court-martial. You warned me of the presence of Sirian agents. I did not listen and as a result my ship was sabotaged."

"The blame is mine, too," Lucky said calmly. "I was on board ship and did not prevent it. Nevertheless, if we can bring back the saboteur, there will be no question of court-martial."

The commander said, "The saboteur, of course, is the robot you warned me of. How I could be so blind!"

"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."