"An infinite number; it is impossible to know. Some differ greatly, some so slightly that it is impossible to mark the difference. Imagine them, if you will, as close together as cards in a pack. If two-dimensional creatures, cluba and hearts, lived on each card, they would be unaware of the other cards and just as unable to reach them. Continue the analogy, drive a nail through all of the cards. Now the other cards can be reached. My people, the 'we' you asked about, are the ones who can do that. We have reached many world lines. Some we cannot reach-some we dare not reach."

"Why?"

"You ask why-after what you saw out there?" For the first time since they had met, Arinix lost his cold detachment. His single eye blazed with fury, and his fists were clenched as he paced the floor. "You saw the filthy things that happen, the death that comes before the absolute death. You see me, and I am typical of my people, maimed, killed, and scarred by a swollen sun that produces more and more hard radiation every year. We escaped our world line, seeking salvation in other world lines, only to discover the awful and ultimate secret. The rot is beginning, going faster and faster all the time. You saw what the world is like beyond that door. Do you understand what I am saying, do the words make any sense to you?

"The sun is going nova. It is the end."

4

"Water," Arinix called out hoarsely, slumping onto the metal bench, his single eye closed now. The inner door opened, and his companion appeared with a pitcher and refilled the glasses. He moved as smoothly as before and seemed ignorant of the black hole in his forehead.

"He is a Sixim," Arinix said, seeing the direction of Mark's gaze. He drank the water so greedily that it ran down his chin. "They are our helpers; we could not do without them. Not our invention. We borrow what we need. They are machines, fabrications of plastic and metal, though there is artificial flesh of some kind involved in their construction. I do not know the details. Their controlling apparatus is somewhere in the armored chest cavity; they are quite invulnerable."

Mark had to ask the question.

"The sun is going nova, you said. Everywhere, in every time line-in my time line?"

Arinix shook his head a weary no. "Not in every line; that is our only salvation. But in too many of them-and the pace is accelerating steadily. Your line-no, not as far as we know. The solar spectrum does not show the characteristic changes. Your line has enough problems as it is, and is one we use for much-needed supplies. There are few of us, always too few, and so much to be done. We must save whom we can and what we can, do it without telling why or how we operate. It is a great work that does not end, and is a most tiring one. But my people are driven, driven insane with hatred, at times, of that bloated, evil thing in the sky. We have survived for centuries in spite of it, maimed and mutated by the radiation it pours out. It was due to a successful mutation that we escaped even as we have, a man of genius who discovered the door between the world lines. But the unsuccessful outnumber a million to one the successful in mutations, and I will not attempt to describe the suffering in my world. You may think me maimed, but I am one of the lucky ones. We have escaped our world line but found the enemy waiting everywhere. We have tried to fight back. We started less than two hundred years ago, and our enemy started millions of years before us. From it we have learned to be ruthless in the war, and we will go on fighting it until we have done everything possible."

"You want me to do something in that world outside the door?"

"No, not there; they are dead. The destruction is too advanced. We can only watch. Closer to the end, we will save what art we can. Things have been noted. We know a culture by its art, don't we? We know a world that way as well. So many gone without record, so much to do."

He drank greedily at the water, slobbering. Perhaps he was mad, Mark thought, partly mad, at least. Hating the sun,trying to fight it, fighting an endlessly losing battle. But… wasn't it worth it? If lives, people, could be saved, wasn't that worth any price, any sacrifice? In his world line, men worked to save endangered species. Arinix and his people worked to save another species-their own.

"What can I do to help?" Mark asked.