I think there might have been at least a hundred of them, and they wound slowly up for what seemed like an age, while my leg and back throbbed and shouted at me. I told them to move on ahead and was helped eventually by Henrietta, who wasn’t Henrietta at all but an ex-physicist from Manchester named Henry who was trying to find meaning in an otherwise empty existence by pretending to be a nun.

We reached the top of the stone steps in due course and entered the lowest tier of the libraries. There were books here in abundance, and Finisterre was already looking through the dusty tomes. I pulled one out at random and found an obscure treatise on accountancy dating from the tenth century. Of interest to those obsessed with the history of finance, but not much of anyone else.

“There is an index here,” said Daisy, pointing to a younger book. “The older stuff is on the top floor.”

“Aeschylus’s The Spirit of Pharos,” murmured Finisterre, peering through the gazetteer, “which is argued to be the first ghost story. Have you read it?”

“Sister Georgia translated it for us,” said Daisy. “It’s not totally rubbish. The ghosts turn out to be the lighthouse keepers in disguise, to prevent people from discovering their illegal trade in stolen amphorae.”

“So that’s where the Scooby-Doo ending originated,” I murmured. “Scholars have been hunting for the primary source of that for years.”

“It’s one of only two known copies anywhere in the world,” said Finisterre, “although the other copy is fragmentary. But you’re right about primary sources: When we discovered the second volume of Aristotle’s Poetics, it ended a lot of academic contention on who devised the format for Columbo.”

“There’s little new in literature,” I added. “For many years William Shatner’s depiction of Kirk in Star Trek was considered unique, until it was discovered that an identical character pops up in Ovid’s Metamorphoses 2: Fat Foreigners Are Funny all the time.”

“Horace wrote truly filthy limericks,” added Mother Daisy. “We recite them on special occasions. There was a very good one about a young man from Australia who painted his arse like a dahlia. Do you want to hear it?”

“No thanks.”

“Well,” said Finisterre, who was in no doubt as to the unique value of the library, “I’d like to catalog all this in situ, then take the books to my team of conservators to be copied and—”

He stopped because there was a sharp report far below in the convent.

“What was that?”

“A shot,” I said, “but then we are in the middle of a firing range.”

“Range fire is softened by distance,” replied Daisy expertly. “closer ones are a crack— and that was a crack. Sister Henrietta, close the scriptorium door and defend the library to the death.”