And an hour later we disembarked at the Mobile base. The Old Man and I had bad coffee and sandwiches in the wardroom of the Fulton, some of the Wave officers had taken Mary and cared for her in the women's quarters. She joined us as we left and seemed entirely normal. I said, "Mary, are you all right?"

She smiled at me. "Of course, darling. Why shouldn't I be?"

A small command ship and an escort took us out of there. I had supposed that we were headed back to the Section offices, or more likely to Washington. I had not asked; the Old Man was in no mood to talk and I was satisfied simply to hold Mary's hand and feel relieved.

The pilot put us into a mountainside hangar in one of those egg-on-a-plate maneuvers that no civilian craft can accomplish-in the sky at high speed, then in a cave and stationary. Like that. "Where are we?" I asked.

The Old Man did not answer but got out; Mary and I followed. The hangar was small, just parking space for about a dozen craft, an arresting platform, and a single launching rack; it contained only two other ships besides ours. Guards met us and directed us on back to a door set in the living rock; we went through and found ourselves in an anteroom. An unseen metallic voice told us to strip off what little we wore. I did not mind being naked but I hated to part with my gun and phone.

We went on inside and were met by a young fellow whose total clothing was an armband showing three chevrons and crossed retorts. He turned us over to a girl who was wearing even less, as her armband had only two chevrons. Both of them noticed Mary, each with typical gender response. I think the corporal was glad to pass us on to the captain who received us.

"We got your message," the captain said. "Dr. Steelton is waiting."

"Thank you, ma'am," the Old Man answered. "The sooner, the better. Where?"

"Just a moment," she said, went to Mary and felt through her hair. "We have to be sure, you know," she said apologetically. If she was aware of the falseness of much of Mary's hair, she did not mention it and Mary did not flinch. "All right," she decided, "let's go." Her own hair was cut mannishly short, in crisp gray waves.

"Right," agreed the Old Man. "No, son, this is as far as you go."

"Why?" I asked.

"Because you dam near loused up the first try," he explained briefly. "Now pipe down."

The captain said, "The officers' mess is straight down the first passageway to the left. Why don't you wait there?"

So I did. On the way I passed a door decorated primly in large red skull-and-crossbones and stenciled with: WARNING-LIVE PARASITES BEYOND THIS DOOR; in smaller letters it added Qualified Personnel Only-Use Procedure "A".

I gave the door a wide berth.

The officers' mess was the usual clubroom and there were three or four men and two women lounging in it. No one seemed interested in my presence, so I found an unoccupied chair, sat down, and wondered just who you had to be to get a drink around this joint. After a time I was joined by a large male extrovert wearing a colonel's insignia on a chain around his neck; with it was a Saint Christopher's medal and an I.D. dog tag. "Newcomer?" he asked.

I admitted it. "Civilian expert?" he went on.

"I don't know about 'expert'," I replied. "I'm a field operative."

"Name? Sorry to be officious," he apologized, "but I'm alleged to be the security officer around here. My name's Kelly."

I told him mine. He nodded. "Matter of fact I saw your party coming in. Mine was the voice of conscience, coming out of the wall. Now, Mr. Nivens, how about a drink? From the brief we had on you, you could use one."

I stood up. "Whom do I have to kill to get it?"

"-though as far as I can see," Kelly went on sometime later, "this place needs a security officer the way a horse needs roller skates. We should publish our results as fast as we get them. This isn't like fighting a human enemy."

I commented that he did not sound like the ordinary brass hat. He laughed and did not take offense. "Believe me, son, not all brass hats are as they are pictured-they just seem to be."

I remarked that Air Marshal Rexton struck me as a pretty sharp citizen.

"You know him?" the colonel asked.

"I don't know him exactly, but my work on this job has thrown me in his company a good bit-I last saw him earlier today."

"Hmm-" said the colonel. "I've never met the gentleman. You move in more rarefied strata than I do, sir."

I explained that it was mere happenstance, but from then on he showed me more respect. Presently he was telling me about the work the laboratory did. "By now we know more about those foul creatures than does Old Nick himself. But do we know how to kill them without killing their hosts? We do not.

"Of course," he went on, "if we could lure them one at a time into a small room and douse them with anesthetics, we could save the hosts-but that is like the old saw about how to catch a bird: naturally it's no trouble if you can sneak up close enough to put salt on its tail. I'm not a scientist myself-just the son of a cop and a cop myself under a different tag-but I've talked to the scientists here and I know what we need. This is a biological war and it will be won by biological warfare. What we need is a bug, one that will bite the slug and not the host. Doesn't sound too hard, does it? It is. We know a hundred things that will kill the slug-smallpox, typhus, syphilis, encephalitis lethargica, Obermeyer's virus, plague, yellow fever, and so on. But they kill the host, too."

"Couldn't they use something that everyone is immune to?" I asked. "Take typhoid-everybody has typhoid shots. And almost everybody is vaccinated for smallpox."

"No good-if the host is immune, the parasite doesn't get exposed to it. Now that the slugs have developed this outer cuticle the parasite's environment is the host. No, we need something the host will catch and that will kill the slug, but won't give the host more than a mild fever or a splitting headache."

I started to answer with some no-doubt brilliant thought when I saw the Old Man standing in the doorway. I excused myself and went to him. "What was Kelly grilling you about?" he asked.

"He wasn't grilling me," I answered.

"That's what you think. Don't you know what Kelly that is?"

"Should I?"

"You should. Or perhaps you shouldn't; he never lets his picture be taken. That's B. J. Kelly, the greatest scientific criminologist of our generation."

"That Kelly! But he's not in the army."

"Reserve, probably. But you can guess how important this laboratory is. Come on."

"Where's Mary?"

"You can't see her now. She's recuperating."

"Is she-hurt?"

"I promised you she would not be hurt. Steelton is the best in his line. But we had to go down deep, against a great deal of resistance. That's always rough on the subject."

I thought about it. "Did you get what you were after?"

"Yes and no. We got a great deal, but we aren't through."

"What were you after?"

We had been walking along one of the endless underground passageways of which the place was made. Now he turned us into a small, empty office and we sat down. The Old Man touched the communicator on the desk and said, "Private conference."

"Yes, sir," a voice answered. "We will not record." A green light came on in the ceiling.

"Not that I believe them," the Old Man complained, "but it may keep anyone but Kelly from playing it back. Now, son, about what you want to know; I'm not sure you are entitled to it. You are married to the girl, but that does not mean that you own her soul-and this stuff comes from down so deep that she did not know she had it herself."

I said nothing; there was nothing to say. He went on presently in worried tones, "Still-it might be better to tell you enough so that you will understand. Otherwise you would be bothering her to find out. That I don't want to happen, I don't ever want that to happen. You might throw her into a bad wingding. I doubt if she'll remember anything herself-Steelton is a very gentle operator-but you could stir up things."