No more than a few weeks old, the baby had a small, crumpled face, and she was sleepy; but when she opened her eyes, they were mother-of-pearl gray. The baby seemed a little agitated: strange hands, my mother would have said. I felt sad for Lucia.

“Yes, she’s beautiful.”

She rubbed her stomach. “How is Daniel?”

“With his parents.”

“I think of him often.”

“What’s wrong with your stomach? … Oh. You’re pregnant again.”

She shrugged and looked away.

I took her arm and found her a place to sit, on a bench carved out of the rock wall.

“Rosa, how did you get her out of the American Hospital?”

Rosa shrugged. “Do you really want the details? … The key was that she wanted to come out, despite everything she says. Didn’t you, child?”

Lucia huddled over her baby, hiding her face.

Rosa said, “I’ve done what you asked, George. Can I talk to him now?”

“Go ahead.”

She turned to the rock wall and raised her voice. “I don’t know why you want to do this, Peter McLachlan. What harm have we done you — or anybody? We are an ancient religious order. We dedicate ourselves to the worship of God, through Mary, the mother of His son. We were founded for benevolent reasons. We educate. We store knowledge that would otherwise be lost. In times of trouble we act as a haven for vulnerable women … You can’t deny any of this.”

“Of course not,” Peter said. “But you don’t see yourself clearly. You can’t, in fact; you’re not supposed to. Rosa, even you, who were born outside, have been here too long. Your conscious purposes — the religion, your communal projects — are just by-products. No, more than that — they are glue to bind you together, dazzling concepts that distract your conscious minds. But they are not what the Order is for. They could be replaced by other goals — cruelty instead of benevolence, futility instead of useful purpose — and the Order would work just as well. The truth is the Order exists only for itself …”

In broken phrases he sketched his beliefs. The Order was an anthill, a mole rat colony, a termite mound, he told her. It was not a human society. “Your handful of mamme-nonne, pumping out infants. Your sterile sisters—”

Rosa frowned. “Celibacy is common in Catholic orders.”

“Not celibate. Sterile, ” he hissed.

She listened to his arguments, her face working.

“And you can’t argue with the reality of Lucia,” he said. “Suppose she walked into a medical office in Manchester. The doctor would think Lucia was extraordinary — and so would you, if not for the fact that you grew up here. You have all been down in this hole for a long time. Time enough for adaptation, selection — evolution, Rosa.”

Lucia looked up at me. “What’s he saying? If I am not human, what am I?”

Rosa touched her hands. “Hush, child. It’s all right …” She paced around, her heels clicking softly on the rock floor. I had no real idea what was going through her mind.

“Suppose it’s true,” she said suddenly. “It’s hard to get my head around this nonsense — but suppose I concede that you’re right. That we have formed a — a sort of self-organizing collective here. Even that, in some way, after all these centuries, we have somehow diverged from the common human stock.”

“You’re waking up,” Peter said.

She snapped, “I don’t think you are in any position to patronize me. Let’s remember that you are the nutcase stuck in a hole in the wall with Semtex stuck up his arse.”

“Go on, Rosa,” I said quickly. “Suppose it’s true. Then what?”

“Then—” She raised her hands, lifted her head to the levels hidden above us, the great underground city. “If this is a new way, maybe it’s a better way. We have found a way to run a society, safely and healthily, with population densities orders of magnitude higher than anything else humans have hit on. What is the purpose of any human society? It is surely to provide a system in which as many people as possible can live out lives as long and healthy and happy and peaceful as possible. Wouldn’t it be better for humankind, and this whole crowded planet, if everyone lived peaceably together as they do here?”

“Little drone, you know too much,” he whispered.

She walked boldly up to the cleft. “Show your face, McLachlan.”

He switched on his torch. His face, eerily underlit, hovered in the shadows, his expression unreadable.

Rosa said, “Suppose you’re right. Suppose we are a new form — your word was Coalescents.”

“Yes.”

“Then shouldn’t you accept us for what we are?” She spread her arms. “What have you found, here in this cave under the Appian Way? Aren’t we Homo superior ?”

He clicked off his torch; his face disappeared into the dark.

Rosa had an intense expression, almost a look of triumph.

I asked, “Did you believe all that?”

She glanced at me. “Not a word. I just want him out of there.” She was formidable indeed, I realized; I felt perversely proud.

Peter whispered again, from the dark. “George, she must have already figured some of this out for herself. Even if she didn’t want to face it. I just put it into words for her. She knew it all the time. Really, she’s too smart for the hive, for her own good.”

“But she’s listening,” I said quickly. “Maybe we should take it easy. Don’t do anything destructive. We’ll get the Order to open up, bring in the health professionals, the social workers …”

“There’s no time for that,” he said.

“Why not?”

“No time …” He fell silent, breathing heavily.

I tiptoed away. “I think he’s tiring,” I said to Rosa.

“Then,” she said, “before he triggers his dead man’s switch by falling asleep, I think you have a decision to make.”

“ I have a decision?”

“I can’t say any more. But perhaps McLachlan will listen to you. You can encourage him to blow us all up. You can persuade him to walk away.” Of course she was right, I saw, horrified; the decision had to be mine. “Just remember,” she said coldly, “that there is a place for you here. Even now, even after you brought this lunatic into our Crypt. This can be your home, too. If you do anything to harm us, then you will lose that choice, too.”

I seemed to smell the pounds of Semtex Peter had lodged somewhere in the rock, sense the great weight of the subterranean city around me, the thousands of lives it contained.

Behind us Lucia sat quietly on her bench, her baby on her lap; her gaze was fixed on its face, as if she wanted to shut us out, a malevolent world that wanted to use and control her and her child, even those of us motivated to save her — and I couldn’t blame her.

Now it was my turn to do some pacing. I tried to ignore the hammering of my heart, the remote stink of the Crypt, and to think clearly.

Did I agree with Peter?

Peter’s theorizing about hives and eusociality was all very well. But the reality of the Crypt, which I felt in my blood, was a good deal warmer than his hostile analysis, a lot more welcoming. And I wasn’t about to argue with Rosa about the Order’s history, and the work it had done over centuries. Whatever Peter said, I felt I had no more right to close that down than to shut down the Vatican.

And then there was Homo superior.

I had seen for myself that Peter’s “Coalescents” were not like other humans. Perhaps they were a more advanced form; perhaps Rosa was right that we would need the warm, fecund discipline of Order living to survive a difficult future on a crowded Earth. In which case, what right did I have to make decisions about their future? … I felt I was losing touch with the world. I drew on the thick, musty air, suddenly longing for a fresh blast of cool oxygen-rich topside atmosphere to clear my head. I was one man, flawed, vulnerable, mortal, woefully ignorant, and these issues escalated above me on every scale. How could I possibly make a decision like this?