“It all reminds me of my own school,” I said uncomfortably.

“I know how you feel; many parents of your generation feel the same. Narrow corridors. Oppressive ceilings.” She sighed. “Doesn’t create the right atmosphere, but not much we can do short of pulling it all down.”

We passed out of the central block. The peripheral buildings were newer, dating from the fifties through to more recent times. I was shown a custom-built library constructed in the eighties, a bright and attractive building within which there seemed to be as many computer terminals as bookshelves. The students worked steadily enough, so far as I could see, though no doubt the presence of the head was an encouragement.

Ms. Gisborne kept up a kind of sales patter. Once the school had been run by a teaching order of nuns. During the comprehensivization of Britain’s schools they had left, or been driven out, depending on your point of view. “Although we still have contacts with them,” Ms. Gisborne said. “And with a number of other Catholic groupings. Since Gina’s time, as I said, we have closed down our preschool section, and merged administratively with a large boys’ school half a mile away. We now provide what would have been called sixth-form support in your day — sixteen- to eighteen-year-olds. Our academic record is good, and …”

I suspected she was as bored with me as I was of her, and that half her mind was elsewhere, engaged with the endless, complex task of running the place.

The most spectacular new building turned out to be a chapel. It had a concrete roof of elaborate curves. It turned out this was intended to model the tents within which Moses’s flock lived while crossing the desert. Beneath that startling roof the interior space was bright, littered with fragments of red and gold from the long stained-glass windows, and there was a smell of incense.

I felt oddly uncomfortable. The school still retained its profoundly religious core, within a shell of reform and renovation, persisting through the decades, an old, dark thing surviving.

Ms. Gisborne seemed to sense my unease, and from that moment in the chapel she grew oddly hostile.

“Tell me — when was the last time you were in a church?”

“Two weeks ago, for my father’s funeral,” I said, a bit harshly.

“I’m sorry,” she said evenly. “Was your parents’ faith strong?”

“Yes. But I’m not my parents.”

“Do you regret having had a Catholic education?”

“I don’t know. It was such a huge part of my life — I can’t imagine how I might have turned out if I hadn’t.”

“You will have left school with a strong moral sense, a sense of something bigger than you are. Even if you reject the answers, you keep the questions: Where did I come from, where am I going? What does my life mean? ” She was smiling, her face strong and assured. “Whether you turn away from the faith or not, at least you have been exposed to its reality and potential. Isn’t that a legacy worth taking away?”

“Do you think your secretary will have finished by now?”

“More than likely. You know, I’m surprised you came here, searching for this mysterious ’sister.’ “

“Why? Where else would I go?”

“To your family, of course. To Gina. Perhaps you aren’t very close. Pity.” She led the way out of the chapel, back across the compound to the main block.

The secretary, Milly, had indeed come up with a stack of old preschool records. Forty years old, they were sheets of yellowed paper, some ruled into columns by hand, closely handwritten or typed, and kept in battered-looking box files. Somewhere there must be similarly dusty fossils of my own school career, I realized bleakly.

Ms. Gisborne riffled through the boxes briskly, running a manicured nail down rows of names. I could see she was getting nowhere. “There’s nobody with the surname Poole in here,” she said. “You can see I’ve looked a year or two to either side of—”

“Perhaps you could try another name. Casella.”

She frowned at me. “What’s that?”

“My mother’s maiden name. Maybe that was how she registered the child.”

She sighed and closed the box file. “I fear we are wasting our time, Mr. Poole.”

“I have the photograph,” I said plaintively.

“But that’s all you have.” She didn’t sound sympathetic. “There are many possible explanations. Perhaps it was a cousin, a more distant relative. Or simply another child, a playmate, with a chance resemblance.”

I struggled to say what I felt. “You must see this is important to me.”

She stared at me, an intimidating headmistress faced by an awkward student. But she turned back to the first of her box files and began again.

It took her five more minutes to find it. “Ah,” she said reluctantly. “ Casella. Rosa Casella, first attended nineteen sixty-two …”

I found my breath was short. Perhaps on some level I hadn’t quite believed in the reality of this lost sibling after all, even given the photograph. But now I had a kind of confirmation. Even a name — Rosa. “What happened to her?”

Ms. Gisborne riffled through a couple of pages. “When she reached primary school age she was transferred — ah, here we are — to an English-language school in Rome …” She read on.

I sat there feeling, of all things, jealous. Why should this mysterious Rosa have had the benefit of an education in some fancy Roman school? Why not me?

Abruptly Ms. Gisborne dropped the pages back in the box file and closed it with a snap. “I’m sorry. This is too irregular. I shouldn’t be telling you this. The connection is only through what you claim was your mother’s maiden name—”

I guessed at another connection. “This school in Rome. Was it run by a Catholic order?”

“Mr. Poole—”

“The Puissant Order of Holy Mary Queen of Virgins?”

“Mr. Poole.” She stood up.

“It was the Order, wasn’t it? That was the name you just read.” It was a strange situation. I couldn’t understand her sudden hostility when we had gotten to the records of the Order. It was as if she were defending it — but why I had no idea. Perhaps she had something to hide. I stabbed in the dark. “Does this school have links to the Order, too? Is that why you’re suddenly so defensive?”

She walked to the door. “Good day to you now.” As if by magic Milly opened the door, apparently waiting to throw me out.

I stood up. “Thanks for your time. And you know — you’re right. I will go see Gina. I should have gone there first.” I smiled, as coldly as I could. “And if I find out anything that embarrasses your school and its murky past you can be sure I’ll broadcast it.”

Ms. Gisborne’s face was as expressionless as a statue’s. “You are an unpleasant and flawed man, Mr. Poole. Good day to you.”

And as the big school door was closed against me, unpleasant and flawed was just how I felt — along with a big dose of good old Catholic guilt.

Guilty or not, on the way home I used my cell phone to book a flight to Miami.