“Unofficially, I’ve been on the case of the Phantoms for a long time. I’ve still got connections all over the place, from my commandant days. A good friend of mine in Istanbul – his name’s Salem, you can meet him when we get there, mon lapin – he was on the trail of one of them. Someone very low down the pecking order, we think, or possibly just a hired hand who didn’t really know who she was working for. Anyway, she was mostly just on lowly errands, and one of them was to post those letters that you saw. Salem used to sneak into her house and make copies of them first, and post the copies to me. We think someone must have seen him getting away one night, though, because they stopped passing messages that way a few weeks ago.

“It’s a very intriguing set-up. They must be paranoid about their phones being tapped, which is how their tiara heist was foiled a while back.” Max remembered this from the paper, and made a mental note to underline this in her notebook. “It’s a good system – the police aren’t going to check every innocent-looking letter going out of Istanbul. But I’ve visited the house that the letters are addressed to, and it’s empty, and no one ever shows up to collect the post. So why are the Phantoms sending letters that don’t seem to be read by anyone? Now, that’s a mystery, and if you can solve that, mon lapin, I’ll buy you all the pastries you can eat.

“Anyway, as you saw, the letters told me that the diamond would be leaving Paris by train yesterday, and heading to Istanbul along our route. Clever idea. There’s too much security on an aeroplane, but they’re better off travelling in public if they can, instead of driving through the middle of nowhere. The police might not have a clue who they are, but you can bet that some other pretty nasty criminals are on to them, and they’d all like that diamond. Travel by train, and no one can surprise you in the middle of the night. Not as easily, anyway.”

Max was sure by now that the police badge was real. It was flawless. And besides, it was just not possible to believe that Sister Marguerite was a liar. She chewed some csiga, and tried to hold all the new information together in her head.

She couldn’t help feeling that they ought to tell someone what they knew. And then it occurred to her that maybe Sister Marguerite had already done that. “Were you the anonymous tip-off? You told the police?”