She rifled through the habit with more urgency. A pocket watch. A crossword book. A sheaf of notes, bound together with an elastic band…

They were brief letters. Max flipped through them, willing them to be innocent, but the evidence was stacked against her. Fort operation will proceed as planned – for a moment this meant nothing to Max, and then she remembered with a sinking heart that Fort was the name of the vault where the heartbreak diamond had been kept – Next target will be HBD – well, it was obvious what that stood for – and there, Remove from Paris to HQ by train, 8th December, 3.55 – and there was a series of times and dates below. They matched Max and Marguerite’s journey exactly.

Before Max could read any further, something was pressed just behind her ear.

“Stay where you are,” hissed Sister Marguerite, “and don’t move a muscle until I say you can.”

5. Breakfast in Budapest

Max froze. She waited to feel fear, and maybe see her life flash before her eyes. To her surprise, she mostly just felt sick with sadness. She had liked Sister Marguerite.

There was fumbling behind her, and then a small torch beam cut through the dark, into Max’s eyes.

“Max?” said Marguerite. She lowered the cold-hard-something. That was the good news. The bad news was that Max could now see it was definitely the gun. She moved out of the torch’s beam and looked at Marguerite, whose long face was drooping in horror.

“Max,” she said, “I am so sorry. I didn’t think—”

But before Max could know what she hadn’t thought, Klaus’s alarm clock was playing “The Sun Has Got His Hat On”, and he was rolling over, creating a small berth-quake. Marguerite whisked the gun and the letters into her pyjama-habit.

“Good morning!” Klaus rumbled.

“Good morning, mon chou,” said Sister Marguerite cheerily.

“Why is everyone shouting?” Ester creaked thunderously into her pillow.

Max should have said, “Help, help, she’s a thief and she’s got a gun.” But she looked at Marguerite, her funny face looking naked and small without its wimple, and found herself saying, “Good morning.”

Then the guard came round with their juice and croissants, and Max still didn’t say “Help, help.” She knew that she should, but something seemed to be sticking in her throat. Instead she picked at her croissant, then went to brush her teeth and collect her thoughts in the tiny train toilet. Celeste was at the window in the corridor again, staring out. Max wondered if she was thinking of the mysterious M.