‘A small white book. Niall Greeves picked it up, had a look. It contained no words apart from “Every bed is narrow”, which meant nothing to Greeves. He assumed the woman had taken it from Kim’s bag, then dropped it during her escape after she was caught in the act. Naturally, being a fan of Kim’s and an honest guy, Greeves wanted to return her property to her. But he didn’t want to interrupt her conversation, so he waited. He considered putting the little book back in her bag, but he didn’t want to look like a rummager himself. When Gabriel Kearns left and Kim was alone, Greeves approached her. He said he sort of froze because he’s such a huge fan, and he couldn’t think what to say. He was afraid he’d sound weird, and the other guy who’d spotted the woman fiddling with Kim’s bag was still hanging around too. In the end, Greeves said, he just passed the book to Kim with an incoherent mumble. She looked at him as if he were a complete freak, apparently.’

‘All right, so his account of the giving of the book matches Kim Tribbeck’s,’ said Proust. ‘Do we assume this short-haired woman is Billy, then?’

‘I believe it’s a strong possibility, sir.’ Sam tried not to show his excitement. ‘Greeves describes the woman as having very short brown hair. Faith Kendell, the woman Kim Tribbeck chatted to outside the hospital while Marion Hopwood was dying, also had very short brown hair. Now that we know Marion was murdered and a white book left in her bed …’

‘You don’t need to spell it out, Sergeant.’ Proust perched on the edge of the nearest desk. His trouser legs rode up to reveal black socks with a pattern of purple fish. ‘I have an alternative hypothesis: Faith Kendell doesn’t exist.’

‘Pardon, sir?’

‘A woman with a different name was planning to kill Kim Tribbeck, but disaster struck: she was caught trying to put a white book in Kim’s handbag and realised that she could be identified if Kim were to turn up dead. So she didn’t kill Kim, but she did shoot four other people and she poisoned Marion Hopwood. She used a false name – Faith Kendell – to protect herself because she was at the RGI on 6 January, not to visit a relative with bone cancer but to murder Granny Marion.’

‘We agree, sir. I was calling her Faith Kendell because we don’t know her real name.’

‘I do,’ said the Snowman. ‘At the start of this conversation, I told you I had a development to report. You waved that aside to make way for your own progess bulletin—’

‘Sir, that’s not quite—’