“It’s all over the papers, mon poulet.” (Poulet is French for “chicken”. Again, it’s a nice thing to call someone. Maybe chickens are noble beasts in France.)

“If only I could read them!” said the man, gesturing to his glasses.

“Not long now.” Marguerite pressed down on the frames, cross-eyed with concentration.

“You’re an absolute star,” said the man. “I’m Rupert, by the way. Rupert Nobes.”

“Marguerite,” said Marguerite, and “Max,” said Max. And then the announcement came on to welcome them to the train, and it was in German first, which Max didn’t speak, and it was announcing stops that she had never heard of. Think about something else, she reminded herself. She stood up, with a swish of her imagined long black coat.

“Sister Marguerite,” she said, “may I explore the train?”

Rupert looked a bit surprised, as if maybe it wasn’t normal to want to explore a train that is the same all the way along. But Sister Marguerite just said, “Off you pop, find us something interesting,” and swung her legs aside to let Max pass.

This was Max’s plan:

Imagining being a detective wasn’t enough to stop the unravelling feeling: she was going to have to really do some detecting to take her mind off things. And besides, she told herself, somebody ought to look properly. Le Goff had done the bare minimum, and if there had really been a tip-off that the diamond was on the train, then surely it was worth a little more investigation.

The first thing a detective needed was suspects. Rupert had to be Suspect Number One, because he had so neatly missed the police, but anyone with half a brain could have got past that inspection. That meant that everyone was a suspect, which was a bit overwhelming. But: if the thief was heading for Istanbul, they would make the same changes as Max and Marguerite. If Max could keep tabs on which of the passengers boarded the next train, that should narrow down the suspect list.

She just needed to know who was on this train first. She took her notebook out of her pocket, and turned to a blank page.

There were quite a lot of seats.

This was fine, because it was a seven-hour journey, and soon Paris suburbs were giving way all too fast to rolling fields and long thin trees, and Max was very happy to have a distraction. If she hadn’t been feeling so jumbled up inside, it would have been fun. She had to be cunning: people don’t appreciate you taking notes while staring at them, so she did a lot of wandering-up-and-down-looking-lost, and then darting into empty seats or tiny train toilets to scribble things down. She laid her pages out like the train carriage, and wrote down something unusual about everyone – like this: