She shook her head; he was certain she repressed a chuckle. "No, Barton, to all questions. The answer is more simple. That cycle is not of Tilaran women. With us, ovulation is voluntary act; only thus can placenta form. On Tilara are no accidental conceptions."

"But-the woman in the cagel" Long since, he had told her of the Tilaran woman, scarred in mind and body by the Demu-how. never guessing that their species might be interfertile, he had succumbed to both their urges and unwittingly brought her to agonizing death in futile, abor- tive childbirth. The telling-of his desperate, unskilled efforts to help, while the Demu stayed hid behind their blind, gray walls and let the woman die-it had not ab- solved his inadvertent guilt, but the sharing helped him to bear it Now Limila touched his face.

"But they took away her control of her mind," she said, "so of course she would ovulate, of instinct Barton! It is not a thing you could have known."

"Yeh, I know," he said. "But I wish to hell I could have."

"Of course you do . . ." And in the ancient, tuneless way, she soothed him.

Later, Barton looked in on the control room. He found Tarleton talking on a four-way hookup, to the other squad- ron commanders. "Sit in, will you. Barton? We're having an argument about how the drive works."

"Sure-hi, everybody. But what's the problem? Slow- boat knows it backwards and forwards, and his doctorate in physics is a lot newer and shinier than my near miss at that brass ring."

"He explained it, all right" said Tarleton. "The trou- ble Is, the rest of us don't speak Higher Math." On the screen, SIobodna grinned. "And the one time I heard you talking about it in plain language, the parts I understood seemed to make sense."

Barton shrugged. "I feel a little like Newton trying to tell Einstein, but okay." He sat; against regulations, he

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set his coffee cup on the ledge below the comm-board.

"Here's how I got it from one of the Bell Labs people when he was drunk enough to talk English. . . .

"The main drive field gets positive traction, on some aspect of space-time that we can't measure or even detect in any other way. The only way we know it's there is that the thing works."

A voice came from the screen. "Tamirov here. A ques- tion: we are above light speed. Where is relativity, time dilation, mass increase?"

"Well, that's the other part of the drive. Ordinarily, when something approaches light speed, what happens is-well, you know about time being at right angles to space?"

"Mathematically, yes," said Estelle Cummings. "But I've never been able to visualize it."

"Join the club," said Barton. "But now cut your idea of space to one dimension-your direction of motion-and think of time as perpendicular to that. Okay?" Cummings'

long, heavy blonde hair rippled with her nod.

"All right. Your time is always at right angles to your space-and everyone else's is to theirs, if you follow me.

But at high speeds, Einstein says, your space vector begins swinging off at an angle, toward everybody else's time vector. And vice versa-your time gets mixed into their space. You see?" '*

"I see where you're heading," said SIobodna- "But you're not there yet."

"Okay," Barton said, "you're still going in the same direction in space, of course, but it's as if you were shoot- ing at an angle and wasting most of your thrust off to one side. And at light speed itself, ordinarily it'd be like push- ing altogether sideways, with no forward thrust at all. Be- cause your space-aad-time vectors would have swung all out of kilter with the velocity.

"So the second part of the drive holds those vectors in line where they belong; that's all. It takes power, sure- but the load is linear with speed; we can handle it And so we don't get any mass increase. The only effect we notice, above light speed, is, that our drive wakes-they still propagate at "c"-become deadly as hell, at close range.

"Did I get it about right, Slowboat?"

"I have to admit it sounds a little funny, Barton, but it

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fits the math." Cummings and Tamirov nodded agreement;

Barton hoped they weren't merely being polite.

"If anyone else is as hungry as I am," said Tarleton, "I move we adjourn." No one objected, so he waved a hand in signoff and cut the circuits. "Ready for lunch,

Barton?"

"For me it's dinner, but I'm with you. I'll just check to see if maybe Umila's hungry, too, and join you in a few minutes."

tie got sidetracked. Outside the control room stood Eeshta. From appearances, the small Demu had been waiting a long time and was prepared to wait even longer.

"Eeshtal What are you doing here?"

"Waiting. Barton, we must talk."

"Sure, sure-I haven't seen enough of you lately, any- way. Just a minute; let's see . . ." Behind Compartment Number Three was a small lounge, intended to keep card games and bull sessions from getting underfoot in the gal- ley. Like many another good intention, this one hadn't worked-coffee went with cards, and a sticky table was small price for it. So, as usual, the lounge was vacant.

They entered and sat.

"Okay, Eeshta. What's it all about?"

"Barton, I worry for my egg-parent. And if not for him, then for you."

"Hishtoo getting cabin fever? Isn't someone bringing him out to walk around awhile every day?" Barton thought of the years he had been caged at Hishtoo's re- search station. No daily walks for Barton-and food that oozed up through the floor. Hishtoo should have it so good. . ..

"He comes out, yes. But his mind, no. I fear; he says strangely to roe-not real, sometimes, I think. But if real -*/ real-I fear even more. For you. Barton, and for Earth."

"Hishtoo's laying on threats, or something?" Barton considered the idea. "Maybe you'd better tell me about it"

"Threats? Closely to that, yes. You know what he said, on first hearing of this fleet."

Barton laughed, not long or with humor. "Yeh. That we animals-had best not disturb the homes of the Demu. But hell, Eeshta-you know we're not on any war of exter- mination. We're simply out to convince your people that

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we are people, too, so lay off the zoo bit and the fancy surgery."

"I know. Barton, and am of agreement. It was not right to cage you, to cut and change Limila and Siewen and the Freak. So many others, too-it is good, I think, that you did not see."

"I saw a couple-no, skip that. But what else about Hishtoo?"

"If he says what is real, no an imagining of his own wishes, then I fear-and you should fear."

"Just what does he say?" Questioning the young Demu about its parent. Barton felt like some kind of Gestapo agent-but what choice did he have?

"He says of Demu history, long long past. How from a far place we came-whether from deep in this galaxy or even from another, is not clear. But Demu came where we are, and wiped away any who would not have us there."

"You mean, if the natives weren't friendly, they got clobbered? Eeshta, we're not exactly primitives, to be overawed by a little technology."

"Not like that. Barton-a terrible war! Not in small space, a few planets only. It was from outside our place that the Demu were attacked. That outside was wiped away; it does not exist"

Yes, he thoughtl Down the Arm from Demu country, the space with no habitable planets. God Almighty! It could be! And if it were, what the hell was he heading the fleet into? What might he be doing to Earth?