And then, as if she had imagined them into life, there were police on the platform. They burst on to the cold grey emptiness quite suddenly, and fanned out, one to each door of the train. From Max’s high-up seat they seemed to move silently, like shadows in their black uniforms. They were so exactly like Max’s daydream that she felt her heart flutter nervously in her stomach, and she had to remind herself that they weren’t really looking for her.

While most of the shadows guarded the train doors, three of them boarded, at the other end of the train to Max. She looked around the carriage: no one else had noticed. They were all too busy muttering and looking at their watches and putting up their eyebrows. But the next moment, the intercom crackled into life, and everybody stopped muttering and put their eyebrows down again to listen.

“Ladies and gentlemen,” said the driver, “we are experiencing a slight delay.”

“We know,” muttered someone. A few people shh-ed him. They shh-ed so loudly that other people had to shh the shh-ers. There were a few seconds of general shh pandemonium.

“Police have reason to believe,” the voice went on, “that a valuable object is being smuggled on this train. All bags will need to be inspected, and we must ask for your full cooperation. We may be here some time.” The intercom crackled off, then back on again, and the driver added, “Sorry about that.”

There was a froth of muttering up and down the carriage, as people agreed with each other that the driver did not sound nearly sorry enough. Max took her brown case out from under her feet and hugged it to her chest. A valuable item on board … could it be?

They were right at the far end of the train, and Max had to wait a long time for anything more to happen. The shadows guarding the doors never moved. While they waited Max and Marguerite got through most of the jelly beans the nun had brought, and Marguerite explained to Max all about how you sew the welt of a shoe to its sole, and they did half the crossword in the newspaper, and the muttering from the other passengers grew ever more mutinous.

At last, there was a tut-PFFFfff behind them. It sounded so much like a tut and a sigh that Max turned around, half-expecting to see her mother; but it was just the sound of the automatic door. And the person who came in was very much not her mother.

He was dressed in a smarter black uniform than the people on the platform, with a long black coat, and a face like a serious egg. Two ordinary officers stood behind him. He cleared his throat and held up a shiny badge.