“Police,” he said, unnecessarily. “Bags, please.” And he began walking up the carriage, inspecting bags and asking questions. The other two officers helped out by staring meaningfully at people, coughing importantly, and occasionally writing in notebooks.

Max stared at them. “What do you think they’re looking for?” she whispered to Marguerite.

“Precisely what I would like to know, mon lapin,” said Sister Marguerite, with enormous satisfaction. “We shall have to ask.”

Max looked uncertainly at the serious-egg man, who was advancing up the aisle. He didn’t look like the sort of person you were meant to ask questions. Something in the set of this man’s jaw told her that uncertainties of any kind were not allowed anywhere near him.

But Sister Marguerite was not going to be put off by a firm jaw and a passing likeness to an egg.

“Good evening, mon chou,” she said, as he approached their seats. “This is all very exciting. What are you looking for?”

Mon chou is French for “my cabbage”. Surprisingly, it is actually quite a nice thing to call someone; but normally someone that you know very well, not stern police officers. The policeman’s jaw got even firmer, and the other two officers stared very meaningfully indeed.

“A stolen item,” he said stiffly. “I am Commandant Le Goff,” he added, to avoid any more chou business.

“Bless you,” said Sister Marguerite. “What kind of stolen item, exactly?”

“I’m afraid I’m not at liberty to say, Sister,” said the Commandant, running an impatient hand through Marguerite’s bag, then reaching out a hand for Max’s. Max thought he seemed faintly bored by the whole situation. But if he was really Commandant Le Goff, then she had just read his name in the newspaper; and that just might mean that something very un-boring was under way.

She handed over her case, and decided that if Sister Marguerite could ask questions, she could too. “Are you looking for the heartbreak diamond?” she asked.

Commandant Le Goff paused mid-reach, leaving his hand to flap around foolishly in mid-air. One of the officers started to nod, but the other one kicked him. “How – ahrrrrm,” said Le Goff. “I am not at liberty to say.”

“Oh, excellent guess, Max! Yes, I read all about that. It was in the papers,” said Sister Marguerite, pointing at the newspaper on their table. The Commandant looked where she pointed, and raised his eyebrows at the houseplant, but didn’t answer. By now he had recovered enough to take Max’s case and start wafting his hand around in it. Max couldn’t help thinking that if she was looking for stolen diamonds, she would do a slightly more thorough job. But Commandant Le Goff seemed keen to move on.

Marguerite was not giving in that easily. “How do you know it’s on our little train, then?”