By the time I got myself all the way awake I thought I was alone. I was lying on a leather couch in a bare white room with huge windows, alternate glass-brick and clear glass. Beyond the clear windows was a view of snow-peaked mountains which turned to pale shadows in the glass-brick.

Habit and memory fitted names to all these; the bare office, the orange flare of the great sun, the names of the dimming mountains. But beyond a polished glass desk, a man sat watching me. And I had never seen the man before.

He was chubby, and not young, and had ginger-colored eyebrows and a fringe of ginger-colored hair around the edges of a forehead which was otherwise quite pink and bald. He was wearing a white uniform coat, and the intertwined caduceus on the pocket and on the sleeve proclaimed him a member of the Medical Service attached to the Civilian HQ of the Terran Trade City.

I didn’t stop to make all these evaluations consciously, of course. They were just part of my world when I woke up and found it taking shape around me. The familiar mountains, the familiar sun, the strange man. But he spoke to me in a friendly way, as if it were an ordinary thing to find a perfect stranger sprawled out taking a siesta in here.

“Could I trouble you to tell me your name?”

That was reasonable enough. If I found somebody making himself at home in my office--if I had an office--I’d ask him his name, too. I started to swing my legs to the floor, and had to stop and steady myself with one hand while the room drifted in giddy circles around me.

“I wouldn’t try to sit up just yet,” he remarked, while the floor calmed down again. Then he repeated, politely but insistently, “Your name?”

“Oh, yes. My name.” It was--I fumbled through layers of what felt like gray fuzz, trying to lay my tongue on the most familiar of all sounds, my own name. It was--why, it was--I said, on a high rising note, “This is damn silly,” and swallowed. And swallowed again. Hard.

“Calm down,” the chubby man said soothingly. That was easier said than done. I stared at him in growing panic and demanded, “But, but, have I had amnesia or something?”

“Or something.”

“What’s my name?”

“Now, now, take it easy! I’m sure you’ll remember it soon enough. You can answer other questions, I’m sure. How old are you?”

I answered eagerly and quickly, “Twenty-two.”

The chubby man scribbled something on a card. “Interesting. In-ter-est-ing. Do you know where we are?”

I looked around the office. “In the Terran Headquarters. From your uniform, I’d say we were on Floor 8--Medical.”

He nodded and scribbled again, pursing his lips. “Can you--uh--tell me what planet we are on?”

I had to laugh. “Darkover,” I chuckled, “I hope! And if you want the names of the moons, or the date of the founding of the Trade City, or something--”

He gave in, laughing with me. “Remember where you were born?”

“On Samarra. I came here when I was three years old--my father was in Mapping and Exploring--” I stopped short, in shock. “He’s dead!”

“Can you tell me your father’s name?”

“Same as mine. Jay--Jason--” the flash of memory closed down in the middle of a word. It had been a good try, but it hadn’t quite worked. The doctor said soothingly, “We’re doing very well.”

“You haven’t told me anything,” I accused. “Who are you? Why are you asking me all these questions?”

He pointed to a sign on his desk. I scowled and spelled out the letters. “Randall ... Forth ... Director ... Department...” and Dr. Forth made a note. I said aloud, “It is--Doctor Forth, isn’t it?”

“Don’t you know?”

I looked down at myself, and shook my head. “Maybe I’m Doctor Forth,” I said, noticing for the first time that I was also wearing a white coat with the caduceus emblem of Medical. But it had the wrong feel, as if I were dressed in somebody else’s clothes. I was no doctor, was I? I pushed back one sleeve slightly, exposing a long, triangular scar under the cuff. Dr. Forth--by now I was sure he was Dr. Forth--followed the direction of my eyes.

“Where did you get the scar?”

“Knife fight. One of the bands of those-who-may-not-enter-cities caught us on the slopes, and we--” the memory thinned out again, and I said despairingly, “It’s all confused! What’s the matter? Why am I up on Medical? Have I had an accident? Amnesia?”

“Not exactly. I’ll explain.”

I got up and walked to the window, unsteadily because my feet wanted to walk slowly while I felt like bursting through some invisible net and striding there at one bound. Once I got to the window the room stayed put while I gulped down great breaths of warm sweetish air. I said, “I could use a drink.”

“Good idea. Though I don’t usually recommend it.” Forth reached into a drawer for a flat bottle; poured tea-colored liquid into a throwaway cup. After a minute he poured more for himself. “Here. And sit down, man. You make me nervous, hovering like that.”

I didn’t sit down. I strode to the door and flung it open. Forth’s voice was low and unhurried.

“What’s the matter? You can go out, if you want to, but won’t you sit down and talk to me for a minute? Anyway, where do you want to go?”

The question made me uncomfortable. I took a couple of long breaths and came back into the room. Forth said, “Drink this,” and I poured it down. He refilled the cup unasked, and I swallowed that too and felt the hard lump in my middle begin to loosen up and dissolve.

Forth said, “Claustrophobia too. Typical,” and scribbled on the card some more. I was getting tired of that performance. I turned on him to tell him so, then suddenly felt amused--or maybe it was the liquor working in me. He seemed such a funny little man, shutting himself up inside an office like this and talking about claustrophobia and watching me as if I were a big bug. I tossed the cup into a disposal.

“Isn’t it about time for a few of those explanations?”

“If you think you can take it. How do you feel now?”

“Fine.” I sat down on the couch again, leaning back and stretching out my long legs comfortably. “What did you put in that drink?”

He chuckled. “Trade secret. Now; the easiest way to explain would be to let you watch a film we made yesterday.”

“To watch--” I stopped. “It’s your time we’re wasting.”

He punched a button on the desk, spoke into a mouthpiece. “Surveillance? Give us a monitor on--” he spoke a string of incomprehensible numbers, while I lounged at ease on the couch. Forth waited for an answer, then touched another button and steel louvers closed noiselessly over the windows, blacking them out. I rose in sudden panic, then relaxed as the room went dark. The darkness felt oddly more normal than the light, and I leaned back and watched the flickers clear as one wall of the office became a large visionscreen. Forth came and sat beside me on the leather couch, but in the picture Forth was there, sitting at his desk, watching another man, a stranger, walk into the office.

Like Forth, the newcomer wore a white coat with the caduceus emblems. I disliked the man on sight. He was tall and lean and composed, with a dour face set in thin lines. I guessed that he was somewhere in his thirties. Dr.-Forth-in-the-film said, “Sit down, Doctor,” and I drew a long breath, overwhelmed by a curious, certain sensation.

I have been here before. I have seen this happen before.

(And curiously formless I felt. I sat and watched, and I knew I was watching, and sitting. But it was in that dreamlike fashion, where the dreamer at once watches his visions and participates in them... )

“Sit down, Doctor,” Forth said, “did you bring in the reports?”

Jay Allison carefully took the indicated seat, poised nervously on the edge of the chair. He sat very straight, leaning forward only a little to hand a thick folder of papers across the desk. Forth took it, but didn’t open it. “What do you think, Dr. Allison?”

“There is no possible room for doubt.” Jay Allison spoke precisely, in a rather high-pitched and emphatic tone. “It follows the statistical pattern for all recorded attacks of 48-year fever ... by the way, sir, haven’t we any better name than that for this particular disease? The term ‘48-year fever’ connotes a fever of 48 years duration, rather than a pandemic recurring every 48 years.”

“A fever that lasted 48 years would be quite a fever,” Dr. Forth said with the shadow of a grim smile. “Nevertheless that’s the only name we have so far. Name it and you can have it. Allison’s disease?”

Jay Allison greeted this pleasantry with a repressive frown. “As I understand it, the disease cycle seems to be connected somehow with the once-every-48-years conjunction of the four moons, which explains why the Darkovans are so superstitious about it. The moons have remarkably eccentric orbits--I don’t know anything about that part, I’m quoting Dr. Moore. If there’s an animal vector to the disease, we’ve never discovered it. The pattern runs like this; a few cases in the mountain districts, the next month a hundred-odd cases all over this part of the planet. Then it skips exactly three months without increase. The next upswing puts the number of reported cases in the thousands, and three months after that, it reaches real pandemic proportions and decimates the entire human population of Darkover.”

“That’s about it,” Forth admitted. They bent together over the folder, Jay Allison drawing back slightly to avoid touching the other man.

Forth said, “We Terrans have had a Trade compact on Darkover for a hundred and fifty-two years. The first outbreak of this 48-year fever killed all but a dozen men out of three hundred. The Darkovans were worse off than we were. The last outbreak wasn’t quite so bad, but it was bad enough, I’ve heard. It has an 87 per cent mortality--for humans, that is. I understand the trailmen don’t die of it.”

“The Darkovans call it the trailmen’s fever, Dr. Forth, because the trailmen are virtually immune to it. It remains in their midst as a mild ailment taken by children. When it breaks out into the virulent form every 48 years, most of the trailmen are already immune. I took the disease myself as a child--maybe you heard?”

Forth nodded. “You may be the only Terran ever to contract the disease and survive.”

“The trailmen incubate the disease,” Jay Allison said. “I should think the logical thing would be to drop a couple of hydrogen bombs on the trail cities--and wipe it out for good and all.”

(Sitting on the Sofa in Forth’s dark office, I stiffened with such fury that he shook my shoulder and muttered, “Easy, there, man!”)

Dr. Forth, on the screen, looked annoyed, and Jay Allison said, with a grimace of distaste, “I didn’t mean that literally. But the trailmen are not human. It wouldn’t be genocide, just an exterminator’s job. A public health measure.”

Forth looked shocked as he realized that the younger man meant what he was saying. He said, “Galactic center would have to rule on whether they’re dumb animals or intelligent non-humans, and whether they’re entitled to the status of a civilization. All precedent on Darkover is toward recognizing them as men--and good God, Jay, you’d probably be called as a witness for the defense! How can you say they’re not human after your experience with them? Anyway, by the time their status was finally decided, half of the recognizable humans on Darkover would be dead. We need a better solution than that.”

He pushed his chair back and looked out the window.

“I won’t go into the political situation,” he said, “you aren’t interested in Terran Empire politics, and I’m no expert either. But you’d have to be deaf, dumb and blind not to know that Darkover’s been playing the immovable object to the irresistible force. The Darkovans are more advanced in some of the non-causative sciences than we are, and until now, they wouldn’t admit that Terra had a thing to contribute. However--and this is the big however--they do know, and they’re willing to admit, that our medical sciences are better than theirs.”

“Theirs being practically non-existent.”

“Exactly--and this could be the first crack in the barrier. You may not realize the significance of this, but the Legate received an offer from the Hasturs themselves.”

Jay Allison murmured, “I’m to be impressed?”

“On Darkover you’d damn well better be impressed when the Hasturs sit up and take notice.”

“I understand they’re telepaths or something--”

“Telepaths, psychokinetics, parapsychs, just about anything else. For all practical purposes they’re the Gods of Darkover. And one of the Hasturs--a rather young and unimportant one, I’ll admit, the old man’s grandson--came to the Legate’s office, in person, mind you. He offered, if the Terran Medical would help Darkover lick the trailmen’s fever, to coach selected Terran men in matrix mechanics.”

“Good Lord,” Jay said. It was a concession beyond Terra’s wildest dreams; for a hundred years they had tried to beg, buy or steal some knowledge of the mysterious science of matrix mechanics--that curious discipline which could turn matter into raw energy, and vice versa, without any intermediate stages and without fission by-products. Matrix mechanics had made the Darkovans virtually immune to the lure of Terra’s advanced technologies.

Jay said, “Personally I think Darkovan science is over-rated. But I can see the propaganda angle--”

“Not to mention the humanitarian angle of healing--”

Jay Allison gave one of his cold shrugs. “The real angle seems to be this; can we cure the 48-year fever?”

“Not yet. But we have a lead. During the last epidemic, a Terran scientist discovered a blood fraction containing antibodies against the fever--in the trailmen. Isolated to a serum, it might reduce the virulent 48-year epidemic form to the mild form again. Unfortunately, he died himself in the epidemic, without finishing his work, and his notebooks were overlooked until this year. We have 18,000 men, and their families, on Darkover now, Jay. Frankly, if we lose too many of them, we’re going to have to pull out of Darkover--the big brass on Terra will write off the loss of a garrison of professional traders, but not of a whole Trade City colony. That’s not even mentioning the prestige we’ll lose if our much-vaunted Terran medical sciences can’t save Darkover from an epidemic. We’ve got exactly five months. We can’t synthesize a serum in that time. We’ve got to appeal to the trailmen. And that’s why I called you up here. You know more about the trailmen than any living Terran. You ought to. You spent eight years in a Nest.”

(In Forth’s darkened office I sat up straighter, with a flash of returning memory. Jay Allison, I judged, was several years older than I, but we had one thing in common; this cold fish of a man shared with myself that experience of marvelous years spent in an alien world!)

Jay Allison scowled, displeased. “That was years ago. I was hardly more than a baby. My father crashed on a Mapping expedition over the Hellers--God only knows what possessed him to try and take a light plane over those crosswinds. I survived the crash by the merest chance, and lived with the trailmen--so I’m told--until I was thirteen or fourteen. I don’t remember much about it. Children aren’t particularly observant.”

Forth leaned over the desk, staring. “You speak their language, don’t you?”

“I used to. I might remember it under hypnosis, I suppose. Why? Do you want me to translate something?”

“Not exactly. We were thinking of sending you on an expedition to the trailmen themselves.”

(In the darkened office, watching Jay’s startled face, I thought; God, what an adventure! I wonder--I wonder if they want me to go with him?)

Forth was explaining: “It would be a difficult trek. You know what the Hellers are like. Still, you used to climb mountains, as a hobby, before you went into Medical--”

“I outgrew the childishness of hobbies many years ago, sir,” Jay said stiffly.

“We’d get you the best guides we could, Terran and Darkovan. But they couldn’t do the one thing you can do. You know the trailmen, Jay. You might be able to persuade them to do the one thing they’ve never done before.”

“What’s that?” Jay Allison sounded suspicious.

“Come out of the mountains. Send us volunteers--blood donors--we might, if we had enough blood to work on, be able to isolate the right fraction, and synthesize it, in time to prevent the epidemic from really taking hold. Jay, it’s a tough mission and it’s dangerous as all hell, but somebody’s got to do it, and I’m afraid you’re the only qualified man.”

“I like my first suggestion better. Bomb the trailmen--and the Hellers--right off the planet.” Jay’s face was set in lines of loathing, which he controlled after a minute, and said, “I--I didn’t mean that. Theoretically I can see the necessity, only--” he stopped and swallowed.

“Please say what you were going to say.”

“I wonder if I am as well qualified as you think? No--don’t interrupt--I find the natives of Darkover distasteful, even the humans. As for the trailmen--”

(I was getting mad and impatient. I whispered to Forth in the darkness, “Shut the damn film off! You couldn’t send that guy on an errand like that! I’d rather--”

(Forth snapped, “Shut up and listen!”

(I shut up and the film continued to repeat.)

Jay Allison was not acting. He was pained and disgusted. Forth wouldn’t let him finish his explanation of why he had refused even to teach in the Medical college established for Darkovans by the Terran empire. He interrupted, and he sounded irritated.

“We know all that. It evidently never occurred to you, Jay, that it’s an inconvenience to us--that all this vital knowledge should lie, purely by accident, in the hands of the one man who’s too damned stubborn to use it?”

Jay didn’t move an eyelash, where I would have squirmed, “I have always been aware of that, Doctor.”

Forth drew a long breath. “I’ll concede you’re not suitable at the moment, Jay. But what do you know of applied psychodynamics?”

“Very little, I’m sorry to say.” Allison didn’t sound sorry, though. He sounded bored to death with the whole conversation.

“May I be blunt--and personal?”

“Please do. I’m not at all sensitive.”

“Basically, then, Doctor Allison, a person as contained and repressed as yourself usually has a clearly defined subsidiary personality. In neurotic individuals this complex of personality traits sometimes splits off, and we get a syndrome known as multiple, or alternate personality.”

“I’ve scanned a few of the classic cases. Wasn’t there a woman with four separate personalities?”

“Exactly. However, you aren’t neurotic, and ordinarily there would not be the slightest chance of your repressed alternate taking over your personality.”

“Thank you,” Jay murmured ironically, “I’d be losing sleep over that.”

“Nevertheless I presume you do have such a subsidiary personality, although he would normally never manifest. This subsidiary--let’s call him Jay_--would embody all the characteristics which you repress. He would be gregarious, where you are retiring and studious; adventurous where you are cautious; talkative while you are taciturn; he would perhaps enjoy action for its own sake, while you exercise faithfully in the gymnasium only for your health’s sake; and he might even remember the trailmen with pleasure rather than dislike.”

“In short--a blend of all the undesirable characteristics?”

“One could put it that way. Certainly he would be a blend of all the characteristics which you, Jay, consider_ undesirable. But--if released by hypnotism and suggestion, he might be suitable for the job in hand.”

“But how do you know I actually have such an--alternate?”

“I don’t. But it’s a good guess. Most repressed--” Forth coughed and amended, “most disciplined personalities possess such a suppressed secondary personality. Don’t you occasionally--rather rarely--find yourself doing things which are entirely out of character for you?”

I could almost feel Allison taking it in, as he confessed, “Well--yes. For instance--the other day--although I dress conservatively at all times--” he glanced at his uniform coat, “I found myself buying--” he stopped again and his face went an unlovely terra-cotta color as he finally mumbled, “a flowered red sports shirt.”

Sitting in the dark I felt vaguely sorry for the poor gawk, disturbed by, ashamed of the only human impulses he ever had. On the screen Allison frowned fiercely, “A crazy impulse.”

“You could say that, or say it was an action of the suppressed Jay_. How about it, Allison? You may be the only Terran on Darkover, maybe the only human, who could get into a trailman’s Nest without being murdered.”

“Sir--as a citizen of the Empire, I don’t have any choice, do I?”

“Jay, look,” Forth said, and I felt him trying to reach through the barricade and touch, really touch that cold contained young man, “we couldn’t order any man to do anything like this. Aside from the ordinary dangers, it could destroy your personal balance, maybe permanently. I’m asking you to volunteer something above and beyond the call of duty. Man to man--what do you say?”

I would have been moved by his words. Even at secondhand I was moved by them. Jay Allison looked at the floor, and I saw him twist his long well-kept surgeon’s hands and crack the knuckles with an odd gesture. Finally he said, “I haven’t any choice either way, Doctor. I’ll take the chance. I’ll go to the trailmen.”

The screen went dark again and Forth flicked the light on. He said, “Well?”

I gave it back, in his own intonation, “Well?” and was exasperated to find that I was twisting my own knuckles in the nervous gesture of Allison’s painful decision. I jerked them apart and got up.

“I suppose it didn’t work, with that cold fish, and you decided to come to me instead? Sure, I’ll go to the trailmen for you. Not with that Allison--I wouldn’t go anywhere with that guy--but I speak the trailmen’s language, and without hypnosis either.”

Forth was staring at me. “So you’ve remembered that?”

“Hell, yes,” I said, “my dad crashed in the Hellers, and a band of trailmen found me, half dead. I lived there until I was about fifteen, then their Old-One decided I was too human for them, and they took me out through Dammerung Pass and arranged to have me brought here. Sure, it’s all coming back now. I spent five years in the Spacemen’s Orphanage, then I went to work taking Terran tourists on hunting parties and so on, because I liked being around the mountains. I--” I stopped. Forth was staring at me.

“You think you’d like this job?”

“It would be tough,” I said, considering. “The People of the Sky--” (using the trailmen’s name for themselves) “--don’t like outsiders, but they might be persuaded. The worst part would be getting there. The plane, or the ‘copter, isn’t built that can get through the crosswinds around the Hellers and land inside them. We’d have to go on foot, all the way from Carthon. I’d need professional climbers--mountaineers.”

“Then you don’t share Allison’s attitude?”

“Dammit, don’t insult me!” I discovered that I was on my feet again, pacing the office restlessly. Forth stared and mused aloud, “What’s personality anyway? A mask of emotions, superimposed on the body and the intellect. Change the point of view, change the emotions and desires, and even with the same body and the same past experiences, you have a new man.”

I swung round in mid-step. A new and terrible suspicion, too monstrous to name, was creeping up on me. Forth touched a button and the face of Jay Allison, immobile, appeared on the visionscreen. Forth put a mirror in my hand. He said, “Jason Allison, look at yourself.”

I looked.

“No,” I said. And again, “No. No. No.”

Forth didn’t argue. He pointed, with a stubby finger. “Look--” he moved the finger as he spoke, “height of forehead. Set of cheekbones. Your eyebrows look different, and your mouth, because the expression is different. But bony structure--the nose, the chin--”

I heard myself make a queer sound; dashed the mirror to the floor. He grabbed my forearm. “Steady, man!”

I found a scrap of my voice. It didn’t sound like Allison’s. “Then I’m--Jay_? Jay Allison with amnesia?”

“Not exactly.” Forth mopped his forehead with an immaculate sleeve and it came away damp with sweat, “No--not Jay Allison as I know him!” He drew a long breath. “And sit down. Whoever you are, sit down!”

I sat. Gingerly. Not sure.

“But the man Jay might have been, given a different temperamental bias. I’d say--the man Jay Allison started out to be. The man he refused to be. Within his subconscious, he built up barriers against a whole series of memories, and the subliminal threshold--”

“Doc, I don’t understand the psycho talk.”

Forth stared. “And you do remember the trailmen’s language. I thought so. Allison’s personality is suppressed in you, as yours was in him.”

“One thing, Doc. I don’t know a thing about blood fractions or epidemics. My half of the personality didn’t study medicine.” I took up the mirror again and broodingly studied the face there. The high thin cheeks, high forehead shaded by coarse dark hair which Jay Allison had slicked down now heavily rumpled. I still didn’t think I looked anything like the doctor. Our voices were nothing alike either; his had been pitched rather high, falsetto. My own, as nearly as I could judge, was a full octave deeper, and more resonant. Yet they issued from the same vocal chords, unless Forth was having a reasonless, macabre joke.

“Did I honest-to-God study medicine? It’s the last thing I’d think about. It’s an honest trade, I guess, but I’ve never been that intellectual.”

“You--or rather, Jay Allison is a specialist in Darkovan parasitology, as well as a very competent surgeon.” Forth was sitting with his chin in his hands, watching me intently. He scowled and said, “If anything, the physical change is more startling than the other. I wouldn’t have recognized you.”

“That tallies with me. I don’t recognize myself.” I added, “--and the queer thing is, I didn’t even like Jay Allison, to put it mildly. If he--I can’t say he, can I?”

“I don’t know why not. You’re no more Jay Allison than I am. For one thing, you’re younger. Ten years younger. I doubt if any of his friends--if he had any--would recognize you. You--it’s ridiculous to go on calling you Jay_. What should I call you?”

“Why should I care? Call me Jason.”

“Suits you,” Forth said enigmatically. “Look, then, Jason. I’d like to give you a few days to readjust to your new personality, but we are really pressed for time. Can you fly to Carthon tonight? I’ve hand-picked a good crew for you, and sent them on ahead. You’ll meet them there. You’ll find them competent.”

I stared at him. Suddenly the room oppressed me and I found it hard to breathe. I said in wonder, “You were pretty sure of yourself, weren’t you?”

Forth just looked at me, for what seemed a long time. Then he said, in a very quiet voice, “No. I wasn’t sure at all. But if you didn’t turn up, and I couldn’t talk Jay into it, I’d have had to try it myself.”

Jason Allison, Junior, was listed on the directory of the Terran HQ as “Suite 1214, Medical Residence Corridor.” I found the rooms without any trouble, though an elderly doctor stared at me rather curiously as I barged along the quiet hallway. The suite--bedroom, minuscule sitting-room, compact bath--depressed me; clean, closed-in and neutral as the man who owned them, I rummaged them restlessly, trying to find some scrap of familiarity to indicate that I had lived here for the past eleven years.

Jay Allison was thirty-four years old. I had given my age, without hesitation, as 22. There were no obvious blanks in my memory; from the moment Jay Allison had spoken of the trailmen, my past had rushed back and stood, complete to yesterday’s supper (only had I eaten that supper twelve years ago)? I remembered my father, a lined silent man who had liked to fly solitary, taking photograph after photograph from his plane for the meticulous work of Mapping and Exploration. He’d liked to have me fly with him and I’d flown over virtually every inch of the planet. No one else had ever dared fly over the Hellers, except the big commercial spacecraft that kept to a safe altitude. I vaguely remembered the crash and the strange hands pulling me out of the wreckage and the weeks I’d spent, broken-bodied and delirious, gently tended by one of the red-eyed, twittering women of the trailmen. In all I had spent eight years in the Nest, which was not a nest at all but a vast sprawling city built in the branches of enormous trees. With the small and delicate humanoids who had been my playfellows, I had gathered the nuts and buds and trapped the small arboreal animals they used for food, taken my share at weaving clothing from the 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.