“Certainly.”

“In a space-skipper? You might—”

“I might,” said Gottstein, “have used Outlet P-4, which is less than a thousand yards from here. Yes, indeed. But I wasn’t looking only for you.”

“Well, I won’t ask for the meaning of what you say.”

“There’s no reason for me to be coy. Surely you have not expected me to be uninterested in the fact that you have been carrying on experiments on the Lunar surface.”

“It’s been no secret and anyone might be interested.”

“Yet no one seems to know the details of the experiments. Except, of course, that in some way you are working on matters concerning the Electron Pump.”

“It’s a reasonable assumption.”

“Is it? It seemed to me that experiments of such a nature, to have any value at all, would require a rather enormous setup. This is not of my own knowledge, you understand. I consulted those who would know. And, it is quite obvious, you are not working on such a setup. It occurred to me, therefore, that you might not be the proper focus of my interest. While my attention was drawn to you, others might be undertaking more important tasks.”

“Why should I be used as distraction?”

“I don’t know. If I knew, I would be less concerned.”

“So I have been under observation.”

Gottstein chuckled. “That, yes. Since you have arrived. But while you have been working here on the surface, we have observed this entire region for miles in every direction. Oddly enough, it would seem that you, Dr. Denison, and your companion, are the only ones on the Lunar surface for any but the most routine of purposes.”

“Why is that odd?”

“Because it means that you really think you’re doing something with your gimcrack contraption, whatever it is. I can’t believe that you are incompetent, so I think it would be worth listening to you if you tell me what you are doing.”

“I am experimenting in para-physics, Commissioner, precisely as rumor has it. To which I can add that so far my experiments have been only partly successful.”

“Your companion is, I imagine, Selene Lindstrom L., a tourist guide.”

“Yes.”

“An unusual choice as an assistant.”

“She is intelligent, eager, interested, and extremely attractive.”

“And willing to work with an Earthman?”

“And quite willing to work with an Immigrant who will be a Lunar citizen as soon as he qualifies for that status.”

Selene was approaching now. Her voice rang in their ears. “Good day, Commissioner. I would have liked not to overhear, and intrude on a private conversation, but, in a spacesuit, overhearing is inevitable anywhere within the horizon.”

Gottstein turned. “Hello, Miss Lindstrom. I did not expect to talk in secrecy. Are you interested in para-physics?”

“Oh, yes.”

“You are not disheartened by the failures of the experiment.”

“They are not entirely failures,” she said. “They are less a failure than Dr. Denison thinks at present.”

“What?” Denison turned sharply on his heel, nearly overbalancing himself and sending out a spurt of dust.

All three were facing the Pionizer now, and above it, just about five feet above it, light shone like a fat star. Selene said, “I raised the intensity of the magnetic field, and the nuclear field remained stable in being—then eased further and further and—”

“Leaked!” Denison said. “Damn it. I didn’t see it happen.”

Selene said, “I’m sorry, Ben. First you were lost in your own thoughts, then the Commissioner arrived, and I couldn’t resist the chance of trying on my own.”

Gottstein said, “But just what is it that I see there?”

Denison said, “Energy being spontaneously given off by matter leaking from another Universe into ours.”

And even as he said that the light blinked out and many yards away, a farther, dimmer star came into simultaneous being.

Denison lunged toward the Pionizer, but Selene, all Lunar grace, propelled herself across the surface more efficiently and was there first. She killed the field structure and the distant star went out.

She said, “The leak-point isn’t stable, you see.”

“Not on a small scale,” said Denison, “but considering that a shift of a light-year is as theoretically possible as a shift of a hundred yards, one of a hundred yards only is miraculous stability.”

“Not miraculous enough,” said Selene, flatly.

Gottstein interrupted. “Let me guess what you’re talking about You mean that the matter can leak through here, or there, or anywhere in our Universe—at random.”

“Not quite at random, Commissioner,” said Denison. “The probability of leakage drops with distance from the Pionizer, and rather sharply I should say. The sharpness depends on a variety of factors and I think we’ve tightened the situation remarkably. Even so, a flip of a few hundred yards is quite probable and, as a matter of fact, you saw it happen.”

“And it might have shifted to somewhere within the city or within our own helmets, perhaps.”

Denison said, impatiently, “No, no. The leak, at least by the techniques we use, is heavily dependent on the density of matter already present in this Universe. The chances are virtually nil that the leak-position would shift from a place of essential vacuum to one where an atmosphere even a hundredth as dense as that within the city or within our helmets would exist. It would be impractical to expect to arrange the leak anywhere but into a vacuum in the first place, which is why we had to make the attempt up here on the surface.”

“Then this is not like the Electron Pump?”

“Not at all,” said Denison. “In the Electron Pump there is a two-way transfer of matter, here a one-way leak. Nor are the Universes involved the same.”

Gottstein said, “I wonder if you would have dinner with me this evening, Dr. Denison?”

Denison hesitated. “Myself only?”

Gottstein attempted a bow in the direction of Selene but could accomplish only a grotesque parody of it in his spacesuit. “I would be charmed to have Miss Lindstrom’s company on another occasion, but on this one I must speak with you alone, Dr. Denison.”

“Oh, go ahead,” said Selene, crisply, as Denison still hesitated. “I have a heavy schedule tomorrow anyway and you’ll need time to worry about the leak-point instability.”

Denison said, uncertainly, “Well, then—-Selene, will you let me know when your next free day is?”

“I always do, don’t I? And we’ll be in touch before then anyway.... Why don’t you two go on? I’ll take care of the equipment.”

Barren Neville shifted from foot to foot in the fashion made necessary by the restricted quarters and by the Moon’s gravity. In a larger room under a world’s stronger pull, he would have walked hastily up and back. Here, he tilted from side to side, in a repetitive back-and-forth glide.

“Then you’re positive it works. Right, Selene? You’re positive?”

“I’m positive,” said Selene. “I’ve told you five times by actual count.”

Neville didn’t seem to be listening. He said in a low, rapid voice, “It doesn’t matter that Gottstein was there, then? He didn’t try to stop the experiment?”

“No. Of course not.”

“There was no indication that he would try to exert authority—”

“Now, Barron, what kind of authority could he exert? Will Earth send a police force? Besides—oh, you know they can’t stop us.”

Neville stopped moving, stood motionless for a while. “They don’t know? They still don’t know?”

“Of course they don’t. Ben was looking at the stars and then Gottstein came. So I tried for the field-leak, got it, and I had already gotten the other. Ben’s setup—”

“Don’t call it his setup. It was your idea, wasn’t it?”

Selene shook her head. “I made vague suggestions. The details were Ben’s.”

“But you can reproduce it now. For Luna’s sake, we don’t have to go to the Earthie for it, do we?”