Max remembered Istvan Marek looking up sharply from the parcel, and how the three of them had shouted after her as she ran. She had thought they were cross with her, but they must have been excited by the name on her great-aunt’s headed paper. It made her feel peculiar to think that they were still there in their soft silent hallway, all those miles away, calling and calling for Elodie Morel. “Um,” she said, “sorry about that. I was investigating.”

“Unlike some people,” added Marguerite, looking pointedly at Le Goff. “Now, what about this reward?”

It turned out that the reward would have to be paid to Max, as nuns aren’t allowed money. But Max didn’t have a bank account.

“Well, I’ll send someone to get it in cash for you, then,” said Le Goff, closing his eyes again and covering up a yawn. “That will be simplest.”

Sister Marguerite opened her mouth to tell him off. Clearly, she didn’t think that handing huge sums of money in cash over to small children was a very thorough way to deal with the situation. But Max kicked her ankle, and mouthed, “Rupert.” If they could give Rupert the cash that he needed, he could return safely to London. So Sister Marguerite shut her mouth again, and settled for pursing her lips instead.

Two hours later, they were setting off back to Salem’s café, carrying two cases. One, bulging and heavy, was for Rupert’s debts. The other, the lighter case, Max was allowed to keep.

“How much did this train journey cost?” Max asked. Sister Marguerite told her. Max did her sums, which made her brain hurt, and she had to do them a few times to be sure. “OK,” she said at last, “then I’m going to go somewhere on a train every school holiday until I’m … until I leave school.”

When they reached the café, Salem was sitting at a table outside, slowly and patiently taking black onyx off a tiny bird, which trembled in his hand. The window was already full of de-jewelled birds, cheeping feebly for joy, and in the alleyway at the side of the café hundreds more cages were waiting.

“This was your doing, Max? Setting me this Herculean task?” said Salem. But he was smiling, and Max knew from the tender way that he stroked the onyx bird that he was pleased. It warbled softly to him.

“I thought you might know what to do for them,” said Max.

“I can try my best. They’ll probably never be able to fly now; but they can be comfortable enough, if I look after them. And they’re already earning their keep.” He nodded down the road, to a young couple walking towards them. “Watch.”