Max reminded herself that suitcases are private business. And she knew that this was what her maman would call “taking your games too far”. But her maman wasn’t there, and detectives had to look into private business sometimes, especially when there was a diamond thief on the loose – and there was no good innocent reason that Max could think of for an old lady’s holiday suitcase to feel like a case full of rocks.

She opened the clasps.

It was disappointing. Layers of fussy silks and laces and old-lady underwear, and a huge stockpile of pear drops. She checked every zip pocket and shook out every stocking, but finally had to admit that the diamond wasn’t there.

Now that she had started, she was too excited to stop. Klaus’s great grey case next. It whined gently as she unzipped it. Lots of soft balls of wool; some great Klaus-sized clothes; and an unnecessary number of socks. Nothing of note. Max had never really suspected Klaus anyway. But she was enjoying herself now, and she couldn’t resist creeping to Rupert’s car and checking his bag, since Le Goff never got the chance.

She opened the car door, quietly. She eased it shut again, quietly, leaving it open a crack to avoid the thud it made when you drew it all the way. She crept out into the corridor, quietly. And when she saw the red-headed woman glaring at her with her blue and green eyes, she even remembered to gasp quietly.

She turned the gasp into a yawn, and tried to stroll casually to the train toilet. The woman’s eyes followed her the whole way, and when she came back out they were waiting, like two watchful night lights, seeing her back to bed. Max walked past as calmly as she could. Why was this woman lurking in the corridor in the middle of the night? What was she up to?

Back in bed, Max waited while the train made a night-time stop at a station, and there was a brief flurry of footsteps and voices. She tried to wait another hour at least, to avoid meeting the woman again. It felt like an eternity. But it was the sort of eternity that ends eventually, and when she peeked out again, the woman had gone. She was now even more curious about the woman than she was about Rupert. She tiptoed to her car, slid the door open, and listened.

“Hello?” she whispered.

Nothing.

There were only three people in here, and it was easy to pick out the woman’s case – the other two were teenagers with hiking backpacks, covered in stickers from all round the world. The woman had a smart black case, and it opened with a surprisingly loud ping. Max ssh-ed it without thinking, remembered it was a suitcase, and felt a bit stupid.