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