“All very well and good, Saul. If— if— there were only one or two diseases, and if we had generations, with millions of people, in which to work all this out.”

“But that’s not the case! Say you’re like that green-colored character up in Hydroponics Two.”

“Old McCue? The one whose skin parasite seems to feed him nutrients made from sunlight?”

“Yeah. Great stuff. But— to quote from your own report— the man’s mind has also been reduced to the level of a moron by a peptide byproduct of that very same fungoid parasite!”

The younger man breathed heavily.

“I’m glad you read my studies,” Saul answered.

Carl snorted. “Besides Jeffers, and Virginia’s computer, you’re the only one who writes anything worth reading, anymore. I’m sure you’ll be more famous than ever, when you send your reports to Earth.”

That made Saul wince. How had he managed to make Carl misunderstand him again? “It’s not like that.”

“Oh? Then how is it, Mr. Great Man of Biology? Tell me! I’ve shown you 1 know plenty, for an amateur. Convince me! Tell me how the hell all these fancy theories about symbiosis are going to make one slice of difference to a tiny, overwhelmed colony, every member of which is a total, certain goner!”

The pause lasted. Saul waited until the other man’s breathing had settled— until Carl had slipped back into the webbing on his side of the desk, glaring at him.

“I already told you, but you weren’t listening,” he said softly. “There is one person on this planetoid who’s in no danger at all. Someone with attributes that make him safe in a totally new way.

“That person is me, Carl.”

For the first time, the full point of the conversation seemed to hit the spacer. He stood up.

“You?”

“Me.” Saul nodded. “My sneezing, my perpetual dripping are only surface features of that ‘negotiation process’ we spoke of. And it seams my immune system is a perfect diplomat. Except for the damage to my reproductive cells, my body has taken all comers almost without trouble. It accepts or rejects every new lifeform in short order, and each one soon finds its own niche.”

There was another silence.

“I am quite serious, Carl.”

“But… how?”

“How?” Saul shook his head. “I only know part of it, as yet. For one thing, I’ve inherited a rare enzyme that some have called N Complex. A dozen or so others on Halley have it too.”

“And are they…”

“More disease resistant? Seems so. But also, there’s something else, something in my blood that got there back when I worked with Simon Percell.”

“Yes?” Carl’s voice was flat now, his expression guarded.

“It’s called a reading unit. We only used the things for a couple of years, until we found better ways to strip and analyze DNA in vivo. Nearly forgot completely about the little things… until I saw them floating around down there, where they’d taken over my spermetic cells.”

Saul shook his head. “Don’t know how they got into me, really. Must’ve stuck myself one day while doing a gene analysis. But however they got there, my body’s using them, somehow.

“Now I think I know why I was so lucky, three decades ago, when I developed the new cyanutes. I didn’t really develop them. My body did.”

The longest silence of them all followed this.

At last Carl spoke.

“I’ve also read psychology, Saul. You know, of course, that claims of invulnerability are symptoms of paranoia?”

Saul shrugged. “I am, in almost every basic sense, completely healthy. Completely. The only one in the colony. You don’t believe me?”

“Of course not! What do you take me for?”

Saul held out his hand. “Take it,” he said casually. After a moment’s hesitation, Carl’s callused fingers wrapped around Saul’s, still soft from so long in the slots.

Carl’s grim smile faded into intense concentration as Saul squeezed, talking on, casually.

“Diseases, microgravity deconditioning, slot fatigue…they’ve pounded all of you down until a drugged Cub Scout could beat any of you with one hand tied.”

Carl’s brow beaded. Obstinately, grunting, he tried to match Saul’s grip.

‘You know you can’t t knish the Nudge Launchers in time, even with all of Virginia’s mechs to help. You need people, and you don’t have ’em, Carl. Two hundred slotted for good, another hundred feeble as kittens—”

He let go and Carl sagged back with a ragged sigh, his eyes wide.

“I didn’t show you this to rub your nose in your weakness, Carl. I only want you to believe it when I say there may be a way. A way to give similar immunity to many, maybe even most of the members of this expedition.

“Carl, we just may not be doomed, after all.”

He said no more. There was no point in talking any longer. When the other man had questions, he would ask them. Let it have time to sink in, he thought.

Right now, Carl’s face was like a statue’s. He stood up— rocky, unsteady— staring at Saul even as he backed away, shaking his head. With one hand he touched the doorplate, spilling phosphor light into the darkened room.

From the hallway, Carl kept staring at him until the door had shut again, cutting off the view, but not the image.

After a moment Saul looked up at the ceiling.

Oh, I know you, Ado-shem, he thought at the bearded, fierce-eyed God of Abraham. Thismorning I opened your gift, tore off the wrapping paper, and looked inside. And just now I showed its frightening beauty to a man who was once a friend.

It looks, at just, like a fine gift. Like the rock that flowed with water for the Hebrew children in the desert. But you and t know that inside the box is another box and another, and more ad infinitum.

And I’m still no closer to an answer to the basic questions, am I!? Where did Halley-Life come from? Did comets seed the Earth, long ago? Or are we only the latest invaders of this little worldlet? How could all of this have happened in the first place?

There was no reply, of course.

He smiled upward, through half a mile of rocky ice, at the stars.

Oh, yes. You will have your joke.

Carl and Virginia sat stiffly in nearby web-chairs. The G-wheel had broken down years ago and subtle side effects of constant low-gravity were showing. The lounge was deserted except for them, its vivid wall weather running unnoticed. A drowsy camel slowly bobbed along the brow of a distant sand dune.

“What I mean is, do you think he’s got all his marbles?” Carl asked flatly.

“Of course Saul is perfectly all right,” she answered indignantly, tension visible in her body language.

I’ve got to remember, she really loves the jerk, Carl thought. Okay, be diplomatic. “I’m worried about his… health.”

Virginia wasn’t having any of it. “You mean you think his discovery is a delusion.”

“Well, it is extreme.” Carl threw his hands into the air and boomed out, “I, Saul Lintz, am a godlike immortal. Immune! Impervious! Kneel, mere mortals!”

“That’s not his attitude.”

“Well, let’s say he comes over as a quiet megalomaniac.”

“He was describing a theory.”

“With himself as prime evidence.”

“Well, yes. Who else aboard has the N-constellation?”

“Good question. You could check the DNA log for the corpsicles.”

Virginia’s eyes shifted a fraction sideways for just an instant, but by now he could read her pretty well. “You already have, right?”

She nodded, knitting her fingers together and staring into them. “There are three others.”

“Good. Easy way to test his theory, right’? Unslot ’em and see if they catch a bug.”

“Saul said the same thing when I told him yesterday.”

“Hmmmm. I wonder why he didn’t mention that little fact to me.”