"Naturally, the Hunter's partnership with me is in the less well organized category. He was never completely sure that he wouldn't do me some harm. We're enough like the other humanoids he's known so that he could recognize and offset my normal immunity reactions in about the same way he was used to, and of course with him there I didn't need them-he could take care of infections, just the same, he would check every few days to make sure his neutralization of my immune response to him hadn't had more general effects, for example, if I got a splinter in my finger he'd wait to make sure my body reacted normally before he cleaned up the intruding bacteria.

A couple of years ago, I failed one of those tests. I got badly infected from a minor scratch, and the Hunter found that my immunity chemistry just wasn't working at all any more. He took its place, of course; there was no danger as long as he was with me. Of course, if anything were to happen to him-" Bob didn't finish, but his parents nodded.

They remembered the circumstances which had caused them to learn about the Hunter-Seever, the island doctor, had been the only one Bob had let into the secret before the police project had been concluded. Bob had bluffed the alien fugitive into leaving his father's body, and destroyed the creature by fire; but the departure had been very hasty. A short time later, Arthur Kinnaird had fallen ill. The symptoms were a blend of pneumonia and meningitis, and Seever had been mystified. Eventually, he and Bob had persuaded the reluctant Hunter to transfer to Arthur Kinnaird's body to investigate.

The problem had been straightforward enough; virus like cells left behind by the fugitive in its hasty departure had lost the control and coordination of an intelligent creature and were simply living without regard for the welfare of their host-the sort of thing, on a much cruder level, which the organism originating them had done and which had made it a criminal by the standards of its species. The Hunter had had no trouble incorporating the units into his own structure. Seever had felt it necessary to give the whole story to Bob's mother, who was quite intelligent enough to recognize and be bothered by any half-truths; and later on, when her husband had regained his senses, he had also been told. Under the circumstances they had little choice about believing, and had eventually come to take the Hunter for granted-even addressing him directly at times, though of course their son had to transmit any answers.

"In a way," Bob went on, “I'm a sort of addict of my symbiont. It's not just the immunity thing, now. Other parts of my personal chemistry keep going hay-wire every few months. Sometimes the Hunter can spot the actual cause and do something about it, sometimes he has to use his own abilities in a way not really related to my own body's handling of the same problem-for example, the way he handles infection by consuming the organisms responsible instead of chemical neutralization.

"He's described the whole thing as a juggling act. As time goes on, he has to devote more and more, effort and attention to keeping my machinery going. Quite often some step he takes interferes with, one or more of the things that he's already doing; or that my own biochemistry is normally doing. Unless we can find some fairly simple key cause for all this and do something effective about it-well, he admits, that sooner or later the juggler is bound to drop a plate."

"I suppose he can't just withdraw entirely and let nature take care of the situation," Mrs. Kinnaird asked.

"Nature isn't that interested in me," her son replied. "The juggling act is just what every living body goes into, and drops out of, sooner or later. Letting things go on their own and shutting eyes and ears may produce 'natural' results, but there's no way to be sure your own survival is included in the meaning of 'natural.' Knowledge is what is needed if you hope for things to go your way."

"But surely the Hunter has the knowledge! You told us he could identify thousands, maybe millions, of chemicals-even unbelievably complex things like proteins-by his own senses. He can produce lots of them deliberately. You once said that if you got diabetes he could take over the making of insulin for you."

"I did, I do, and he does. He can do a lot. He is doing a lot, but he has his limits, and they're a long way short of complete takeover of the chemical machinery of a human body. What you miss is the fact that, unbelievable as his abilities are, the complexity of the problem is even more unbelievable. You're more realistic than the weirdoes who think you can heal a burn by shining the proper color of light on it, but you're still not really in touch with the problem."

"Then this weakness of yours is a continuing thing?" Bob's father asked.

"Not exactly-that is, I'm not weak and tired all time. One of the plates that's slipping has something to do with my muscles. The Hunter can't spot anything specifically wrong with them, or with their individual cells, or with the way the cells are interacting and using food, or with the nerves connected with them; but after I've started to get tired-only a little tired, or what should make me only a little tired, they just lose power. The Hunter not only can't sense the cause, he can't even provide a makeshift remedy like delivering sugar or other necessities to the cells directly-it doesn't work. It isn't a matter of getting more fuel to the cells, or running stronger messages along the nerves, or a lot of other things-he could tell us thousands of things it isn't."

There was silence for many minutes.

The older people could not, of course, believe that there was no solution to the problem. This was their child. No longer really a child, and not even their only one, but theirs. They had taken for granted that he would still be alive when their own jugglers dropped the last plate. They would have been embarrassed to say aloud that there had to be an answer, but neither could think along any other line. Neither thought consciously of blaming the Hunter for what had happened, though the wife thought fleetingly that it would have been nice if the alien had chosen to take up existence with the doctor after completion of his police project-Seever might have been able to take effective steps while the problem was still simple. She never brought this point up aloud, however. It was she who finally broke the silence. "What do you and the Hunter plan to do, now that you're here?" she asked. ''You must have a plan- you'd be looking even worse than you do, without one."

"Do you really think Ben Seever can do anything?" was Arthur Kinnaird's contribution. "He can't possibly know as much as the Hunter, even if he is a doctor rather than a detective."

Bob nodded basic agreement with the point; it was one he and the Hunter had considered long before.

"I don't know what he can do, Dad, but we can't help being better off with him than without him. We're telling him the whole story tomorrow. I'd have to see him anyway, since I'll be expected to have a checkup before reporting to work; tomorrow's Friday, and I'm sure PFI will expect my muscles to be available Monday. If nothing else, Doc may be able, to think of something which will keep me out of heavy-muscle work. If I don't do anything useful at all, they'll want to send me to the States or Japan for a real medical going-over, and we've got to stay here." "Why?" both parents asked at once. Bob smiled. "Don't give up when you first hear it. The basic assumption may be wrong, but at least it's not ridiculous. Our first job is to find one or both of the ships that crashed near Ell nearly eight years ago. What do you know about self-contained diving gear, Dad?"

Arthur Kinnaird, quite predictably, ignored the question and put one of his own.

"What good will the ships do? Are there supposed to be medical supplies in them? Would anything useful have lasted this long under water?"