Even after this smooth patter she stayed out of focus. Thinking over what she had said, I found I couldn’t visualize her school, or even the kind of social conditions she had been brought up in — not a family, that was for sure.

She began to talk about the Order’s business. “Yes, we sell genealogy information. I brought some stuff for you to see …” She dug some promotional literature out of her bag: glossy, well produced. Tracing ancestry was one of the biggest growth areas on the Internet, she told me. “We’re even offering a DNA matching service,” she said. “If you’re of British ancestry, say, you’ll soon be able to tell whether you are of ancient stock, or came over with the Romans, or the Saxons, or the Vikings.

“There is a finite genealogical universe out there. Only a finite number of human beings have ever existed, and each of them had a mother and father, links to the great chain of descent. We see no limit in principle as to the information we may one day retrieve …” She was quite evangelical as she described all this. It was more than just a product to her, I saw.

But I felt as if she were pitching a sale. I didn’t know how brother and sister were supposed to behave, after a forty-year separation. It isn’t a situation you come across every day. But for sure it wasn’t talking about DNA databases and high-speed Internet access options.

Actually, as she talked, she reminded me of Gina. Something about her cold competence, her distance from me.

I put aside the brochures. “You’re telling me about genealogy,” I said. “Not you.”

She sat back. “Then what do you want to know?”

“You never came home.”

She nodded. “But this is home, George. This is family, for me.”

“It may feel like that, but—”

“No.” Again she covered my hand, shockingly casual. “You don’t understand. The Order is family — our family. That’s why Father was happy to send me here.” And she reminded me of our story of the ancient past, of Regina, who had survived the collapse of Britain, and who had eventually come to Rome — where she had helped found the Order.

I was tired of this story. “That’s just a family legend,” I said. “Nobody can trace back to the Romans …”

“ We can.” She grinned, almost playfully. “We keep records, George. That’s the one thing we do better than anything else. Our huge bank of historical data is the spine on which we have built our genealogy business. George, it’s true about Regina. There has been a continuous thread of descent, from Regina’s day to this, as the Order has survived. But that central line of family persists. And it’s our family.

“Maybe now you can see why I stayed here.” Again she touched me, unexpectedly. She slid one hand under my palm, and let the other rest on top, massaging the webbing between my thumb and forefinger with the ball of her thumb. It was extraordinarily intimate — not sexual — compelling, oddly confining. She said, “So that’s why you don’t need to rescue me.”

“What do you mean?”

She laughed. “Come on, George. Isn’t that why you’re really here? To save me from my miserable exile. Perhaps on some level you were expecting to find the little girl you last saw, all those years ago. And I’ve somehow disappointed you by turning out to be a grown woman, with a life of her own, and capable of making her own choices. I don’t need saving, as you can see.”

I said angrily, “Okay. Maybe I’m a patronizing dope with no imagination. But I’m here, Rosa.”

She surprised me by standing up. “But we each have our own lives, George. Well, that’s that.” She began extracting money from a small billfold. “Let me treat you,” she said. “I insist.”

I stood uncertainly. I hadn’t been in control of any of this conversation, I realized, from first to last. “Is that it?”

“We must stay in touch. Isn’t email marvelous? How long are you in Rome?—”

“Rosa, for Christ’s sake.” I struggled briefly for control. “Don’t we have any more to say to each other? After all this time?”

She hesitated. “You know, some said I shouldn’t see you.”

“Some who?”

“People in the Order.”

“You told them about me?”

“We tell each other everything.”

“Why shouldn’t you have met me?”

“Because you might be a threat,” she said simply. Her gaze was fixed on me. “But now I’ve met you I’m not so sure.”

I had the impression she was recalculating.

She had felt impelled to go through with the meeting with me, to give me the minimum contact required to send me away, and keep me away. But now something — my persistence, maybe my distress — was making her rethink that plan. I know that’s a cold analysis of her thinking. But I really didn’t believe, even then, that whatever new plans she was drawing up had anything to do with compassion.

She made an abrupt about-face. “Maybe you’re right. It shouldn’t end here. As you said, you came all this way, did all that detective work, for me.” Her eyes narrowed, and I thought she was making a decision. “Tell you what. Perhaps you’d like to see where I work, and live. What do you think?” She dropped her sunglasses onto her nose, businesslike.

She was following her own peculiar agenda, I saw. I really didn’t know what she wanted of me. But it was a chance to spend a little more time with her. What else could I do but accept?

And so she took me to the Catacombs.

The entrance wasn’t far away. Aboveground there was little to see: a very small chapel, a couple of souvenir and refreshment stalls, a ticket booth, all set in a little scruffy parkland. It was lunchtime and the public areas were locked up, the ticket booth windows covered with CHIUSO notices: this was Rome, after all. But a few bewildered-looking tourists lingered by the refreshment stalls, buying overpriced hot dogs and bottled water.

They watched enviously as Rosa led me to a small stone block, the size and shape of Doctor Who ’s TARDIS. It had a heavy green door, which she opened with a swipe card. This was the public entrance to the Catacombs of Agrippina, Rosa told me. She palmed a switch, and electric light flooded down from strip lights set in the ceiling.

Steps cut down into the dark. Rosa led the way, her heeled shoes clattering on the worn stone steps. When I pulled the door closed after me, it locked automatically. It immediately felt colder. It was a creepy experience, even in the electric light.

At the bottom of the steps I found myself in a gallery. It was narrow enough for me to reach out and touch both walls, and it was tall, perhaps twenty-five feet high, with an arched roof. The walls were notched, with box-shaped cavities cut deep into them. The light was dim, the electric lamps sparsely scattered. There was more light, in fact, coming from the skylight trenches cut down from the surface.

Rosa gave me the guided tour. “People say they’ve never heard of a Saint Agrippina. There never was one, so far as we know. She was probably just a well-off local matron, sympathetic to the Christians’ cause, who gave them the use of her land …”

Burials had given the early Christian community here a problem. Space was always at a premium in Rome. Because of their beliefs the Christians were reluctant to cremate, but land was expensive, even this far out of town. So they began to dig.

“The rock here is tufa,” Rosa said. “Soft, volcanic. It’s easy to work, and it hardens when exposed to the air. And the Romans were used to working underground anyhow. They would dig sewers, waterworks, underground passages for servants to cross from one side of a great villa to another. Many houses would even have a cryptoporticus, an underground recreation area. So when they needed a place to bury their dead the Christians dug, and dug …”