fibres of parasite plants cultivated on the stems, and in all those eight years I had set foot on the ground less than a dozen times, even though I had travelled for miles through the tree-roads high above the forest floor.

Then the Old-One's painful decision that I was too alien for them, and the difficult and dangerous journey my trailmen foster-parents and foster-brothers had undertaken, to help me out of the Hellers and arrange for me to be taken to the Trade City. After two years of physically painful and mentally rebellious readjustment to daytime living, the owl-eyed trailmen saw best, and lived largely, by moonlight, I had found a niche for myself, and settled down. But all of the later years (after Jay Allison had taken over, I supposed, from a basic pattern of memory common to both of us) had vanished into the limbo of the subconscious.

A bookrack was crammed with large microcards; I slipped one into the viewer, with a queer sense of spying, and found myself listening apprehensively to hear that measured step and Jay Allison's falsetto voice demanding what the hell I was doing, meddling with his possessions. Eye to the viewer, I read briefly at random, something about the management of compound fracture, then realized I had understood exactly three words in a paragraph. I put my fist against my forehead and heard the words echoing there emptily; "laceration ... primary efflusion ... serum and lymph ... granulation tissue...." I presumed that the words meant something and that I once had known what. But if I had a medical education, I didn't recall a syllable of it. I didn't know a fracture from a fraction.

In a sudden frenzy of impatience I stripped off the white coat and put on the first shirt I came to, a crimson thing that hung in the line of white coats like an exotic bird in snow country. I went back to rummaging the drawers and bureaus. Carelessly shoved in a pigeonhole I found another microcard that looked familiar; and when I slipped it mechanically into the viewer it turned out to be a book on mountaineering which, oddly enough, I remembered buying as a youngster. It dispelled my last, lingering doubts. Evidently I had bought it before the personalities had forked so sharply apart and separated, Jason from Jay. I was beginning to believe. Not to accept. Just to believe it had happened. The book looked well-thumbed, and had been handled so much I had to baby it into the slot of the viewer.

Under a folded pile of clean underwear I found a flat half-empty bottle of whiskey. I remembered Forth's words that he'd never seen Jay Allison drink, and suddenly I thought, "The fool!" I fixed myself a drink and sat down, idly scanning over the mountaineering book.

Not till I'd entered medical school, I suspected, did the two halves of me fork so strongly apart ... so strongly that there had been days and weeks and, I suspected, years where Jay Allison had kept me prisoner. I tried to juggle dates in my mind, looked at a calendar, and got such a mental jolt that I put it face-down to think about when I was a little drunker.

I wondered if my detailed memories of my teens and early twenties were the same memories Jay Allison looked back on. I didn't think so. People forget and remember selectively. Week by week, then, and year by year, the dominant personality of Jay had crowded me out; so that the young rowdy, more than half Darkovan, loving the mountains, half-homesick for a non-human world, had been drowned in the chilly, austere young medical student who lost himself in his work. But I, Jason—I had always been the watcher behind, the person Jay Allison dared not be? Why was he past thirty—and I just 22?

A ringing shattered the silence; I had to hunt for the intercom on the bedroom wall. I said, "Who is it?" and an unfamiliar voice demanded, "Dr. Allison?"

I said automatically, "Nobody here by that name," and started to put back the mouthpiece. Then I stopped and gulped and asked, "Is that you, Dr. Forth?"

It was, and I breathed again. I didn't even want to think about what I'd say if somebody else had demanded to know why in the devil I was answering Dr. Allison's private telephone. When Forth had finished, I went to the mirror, and stared, trying to see behind my face the sharp features of that stranger, Doctor Jason Allison. I delayed, even while I was wondering what few things I should pack for a trip into the mountains and the habit of hunting parties was making mental lists about heat-socks and windbreakers. The face that looked at me was a young face, unlined and faintly freckled, the same face as always except that I'd lost my suntan; Jay Allison had kept me indoors too long. Suddenly I struck the mirror lightly with my fist.

"The hell with you, Dr. Allison," I said, and went to see if he had kept any clothes fit to pack.

Dr. Forth was waiting for me in the small skyport on the roof, and so was a small 'copter, one of the fairly old ones assigned to Medical Service when they were too beat-up for services with higher priority. Forth took one startled stare at my crimson shirt, but all he said was, "Hello, Jason. Here's something we've got to decide right away; do we tell the crew who you really are?"

I shook my head emphatically. "I'm not Jay Allison; I don't want his name or his reputation. Unless there are men on the crew who know Allison by sight—"

"Some of them do, but I don't think they'd recognize you."

"Tell them I'm his twin brother," I said humorlessly.

"That wouldn't be necessary. There's not enough resemblance." Forth raised his head and beckoned to a man who was doing something near the 'copter. He said under his breath, "You'll see what I mean," as the man approached.

He wore the uniform of Spaceforce—black leather with a little rainbow of stars on his sleeve meaning he'd seen service on a dozen different planets, a different colored star for each one. He wasn't a young man, but on the wrong side of fifty, seamed and burly and huge, with a split lip and weathered face. I liked his looks. We shook hands and Forth said, "This is our man, Kendricks. He's called Jason, and he's an expert on the trailmen. Jason, this is Buck Kendricks."

"Glad to know you, Jason." I thought Kendricks looked at me half a second more than necessary. "The 'copter's ready. Climb in, Doc—you're going as far as Carthon, aren't you?"

We put on zippered windbreaks and the 'copter soared noiselessly into the pale crimson sky. I sat beside Forth, looking down through pale lilac clouds at the pattern of Darkover spread below me.

"Kendricks was giving me a funny eye, Doc. What's biting him?"

"He has known Jay Allison for eight years," Forth said quietly, "and he hasn't recognized you yet."

But we let it ride at that, to my great relief, and didn't talk any more about me at all. As we flew under silent whirring blades, turning our backs on the settled country which lay near the Trade City, we talked about Darkover itself. Forth told me about the trailmen's fever and managed to give me some idea about what the blood fraction was, and why it was necessary to persuade fifty or sixty of the humanoids to return with me, to donate blood from which the antibody could be, first isolated, then synthesised.

It would be a totally unheard-of thing, if I could accomplish it. Most of the trailmen never touched ground in their entire lives, except when crossing the passes above the snow line. Not a dozen of them, including my foster-parents who had so painfully brought me out across Dammerung, had ever crossed the ring of encircling mountains that walled them away from the rest of the planet. Humans sometimes penetrated the lower forests in search of the trailmen. It was one-way traffic. The trailmen never came in search of them.

We talked, too, about some