Surprised, I said that I was and asked him where he had learned Spanish. He arched his eyebrows, as if looking into the distant past, and said he’d learned it many years ago.

“My first wife was from Buenos Aires.” He held out his hand. “I’m Arthur Seldom.”

At that time few names could have provoked more admiration in me. The man with the small, pale eyes holding out his hand was already a legend among mathematicians. I’d spent months studying his most famous work, the philosophical extension of Godel’s theorem from the thirties, for a seminar. He was considered one of the four leading minds in the field of logic, and you just had to glance at the varied titles of his work to see that he was a rare case of mathematical genius. Beneath that high, serene forehead some of the most profound ideas of the century had fallen into place. On my second visit to the bookshops in town I had tried to get hold of his latest book, a popular work explaining logical series, and found, to my surprise, that it had been sold out for a couple of months. Someone mentioned that, since the book’s publication, Seldom had disappeared from the conference circuit and apparently nobody dared venture a guess as to what he was working on now. In any case I didn’t even know he lived in Oxford, and I certainly never would have expected to bump into him at Mrs Eagleton’s front door. I told him I’d expounded on his theorem at a seminar and he seemed pleased by my enthusiasm. But he was obviously worried about something as he kept glancing at the door.

“Mrs Eagleton should be in, shouldn’t she?” he said.

“I would have thought so,” I said. “There’s her electric wheelchair. Unless someone’s taken her out by car.”

Seldom rang the bell again and listened at the door. He went to the window that looked on to the hall, and peered inside.

“Is there a back door?” And then, in English, he said: “I’m worried something might have happened to her.”