Bigman pumped a deep breath into his lungs and said, "I never thought you could use a fusion jet to melt a way into a world ahead of a speeding ship."

"You couldn't ordinarily, Bigman," said Lucky. "It just so happens that Mimas is a special case. And so is Enceladus, the next satellite out."

"How come?"

"They're just snowballs. Astronomers have known that since even before space travel. Their density is less than water and they reflect about eighty per cent of the light that hits them, so it's quite obvious they could only be snow, plus some frozen ammonia, and not too tightly packed at that."

"Sure," said Wess, chiming in. "The rings are ice and these first two satellites are just collections of ice that were too far out to make up part of the rings. That's why Mimas melted so easily."

Lucky said, "But we've got a good deal of work to do. Let's start."

They were in a natural cavern formed by the heat of the fusion jet and closed in on all sides. The tunnel they had formed as they entered had closed as they passed, the steam condensing and freezing. The mass detector yielded figures that indicated them to be about one hundred miles below the surface of the satellite. The mass of ice above them, even under Mimas's feeble gravity, was slowly contracting the cavern.

Slowly The Shooting Starr burrowed outward once more, like a hot wire poking into butter, and when they had reached a point within five miles of the surface, they stopped and set up an oxygen bubble.

As a power supply was laid in along with algae tanks and a food supply, Wess shrugged resignedly and said, "Well, this is going to be home for me for a while; let's make it comfortable."

Bigman had just awakened from his sleeping period. He screwed his face into a look of bitter condemnation.

Wess said, "What's the matter, Bigman? All weepy because you're going to miss me?"

Bigman snarled and said, "I'll manage. In two, three years I'll make it a point to whizz by Mimas and drop you a letter." Then he burst out, "Listen, I heard you talking while you thought I was safely asleep. What's the matter? Council secrets?"

Lucky shook his head uneasily. "All in good time, Bigman."

Later, when Lucky was alone with Bigman in the ship, the Councilman said, "Actually, Bigman, there's no reason you can't stay behind with Wess."

Bigman said grumpily, "Oh, sure. Two hours cooped up with him and I'd just chop him into cubes and put him on ice for his relatives." Then he said, "Are you serious, Lucky?"

"Rather serious. What's coming may be more dangerous for you than for me."

"So? What do I care about that?"

"If you stay with Wess then, whatever happens to me, you'll be picked up within two months."

Bigman backed away. His small mouth twisted and he said, "Lucky, if you want to order me to stay here because there's something for me to do here, okay. I'll do it, and when it's done I'll join you. But if you just want me to stay here to be safe while you go off into danger, we're finished. I'll have nothing more to do with you; and without me, you overgrown cobber, you won't be able to do a thing, you know you won't." The Martian's eyes blinked rapidly.

Lucky said, "But, Bigman… "

"All right, I'll be in danger. Do you want me to sign a paper saying it's my own responsibility and not yours? All right, I will. Does that satisfy you, Councilman?"

Lucky seized Bigman's hair affectionately and tugged his head back and forth. "Great Galaxy, trying to do you a favor is like shoveling water."

Wess came into the ship and said, "The still is all set up and working."

Water from the ice substance of Mimas itself poured into The Shooting Starr's reservoirs, filling them and replacing the water lost in cooling the ship's skin during the boring into Mimas. Some of the separated ammonia was carefully neutralized and stored in a skin compartment where it would be available to the algae tanks as nitrogenous fertilizer.

And then the bubble was done and the three of them looked about at the neatly curving ice and at the almost comfortable quarters held within.

"Okay, Wess," Lucky said at last, shaking hands firmly. "You're all set, I think."

"As far as I can tell, Lucky, I am."

"You'll be taken off within two months, no matter what. You'll be taken off much sooner if things break right."

"You're assigning me this job," said Wess coolly, "and it will be done. You concentrate on yours and, by the way, take care of Bigman. Don't let him fall out of his bunk and hurt himself."

Bigman shouted, "Don't think I don't follow all this big-shot mystery talk. You two have a deal on and you're not telling me… "

"Into the ship, Bigman," said Lucky, picking the Martian up bodily and moving him forward, while Bigman squirmed and tried to call out an answer.

"Sands of Mars, Lucky," he said, once they were aboard. "Look what you did. It's bad enough you're keeping your darned Council secrets, but you also let the cobber have the last word."

"He's got the hard job, Bigman. He's got to stay put while we go out and stir up trouble, so let him have the satisfaction of the last word."

They nudged out of Mimas at a spot from which neither Sun nor Saturn was visible. The dark sky held no object larger than Titan, low on one horizon and only a quarter of the apparent diameter of Earth's Moon.

Its globe was half lit by the Sun, and Bigman looked somberly at its image in the visiplate. He had not regained his ebullience. He said, "And that's where the Sirians are, I suppose."

"I think so."

"And where do we go? Back to the rings?"

"Right."

"And if they find us again?"

It might have been a signal. The reception disk glowed to life.

Lucky looked disturbed. "They find us with too little trouble."

He threw in contact. This time it was no dead robotic voice counting off the minutes. It was a sharp voice, instead; a vibrant one, full of life, and a Sirian voice unmistakably.

"-rr, please answer. I am trying to make contact with Councilman David Starr of Earth. Will David Starr please answer? I am trying… "

Lucky said, "Councilman Starr speaking. Who are you?"

"I am Sten Devoure of Sirius. You have ignored the request of our automated ships and returned to our planetary system. You are therefore our prisoner."

Lucky said, "Automated ships?"

"Robot-run. Do you understand that? Our robots can handle ships quite satisfactorily."

"So I have found," said Lucky.

"I think you have. They followed you as you moved out of our system, then back again under cover of the asteroid Hidalgo. They followed you in your movement out of the Ecliptic to Saturn's south pole, then through Cassini's division, under the rings, and then into Mimas. You never once slipped our watch."

"And what made your watch so efficient?" demanded Lucky, managing to keep his voice flat and unconcerned.

"Ah, trust an Earthman not to realize that Sirians might have their own methods. But never mind that We've waited days for you to come out of your Mimas hole after your so clever entry by hydrogen fusion. It amused us to let you hide. Some of us have even made bets on how long it would take you to poke your nose out again. And meanwhile we have carefully surrounded Mimas with our ships and their efficient robot crews. You can't move a thousand miles without being blasted out of space, if we choose."

"Surely not by your robots, which cannot inflict harm on humans."

"My dear Councilman Starr," came the Sirian voice with an unmistakable edge of mockery, "of course robots will not harm human beings if they happen to know that human beings are there to harm. But you see, the robots in charge of the weapons have been carefully instructed that your ship carries robots only. They have no compunction about destroying robots. Won't you surrender?"