Because William Skirmish’s ‘victim timeline’ had become barely relevant to the case, the job of completing it had been handed to the Murder Team’s most junior member, i.e. Lesley. Since she’d spent such a lot of time and effort reconstructing William Skirmish’s last hours she was perfectly willing, in fact overjoyed, to share it with me in excruciating detail. She’d checked out William Skirmish’s romantic leanings and found no history of trawling the West End for sex – serially monogamous, that was our William – all of them guys he’d met through work or mutual friends. She’d also traced every single CCTV that he’d passed that night, and as far as Lesley could tell he’d walked from his house to Tufnell Park Station and caught the tube to Tottenham Court Road – from there, he’d walked straight to Covent garden, via Mercer Street, and his fatal encounter with Coopertown. No deviation or hesitation – as if he had an appointment.

‘Almost as if something was messing with his head,’ she said. ‘Right?’

So I told her about the dissimulo spell and the theory that something had invaded Coopertown’s mind, forced him to change his face, kill William Skirmish and then his family. This led, naturally, to a description of my visit to Mama Thames, the magic lessons and Molly the ‘God knows what she is’ Maid.

‘Should you be telling me this?’ asked Lesley.

‘I don’t see why not,’ I said. ‘Nightingale’s never told me not to. Your boss believes this stuff is real, too; he just doesn’t like it very much.’

‘So something was messing with Coopertown’s mind – right?’ asked Lesley.

‘Right,’ I said.

‘And whatever that was,’ continued Lesley, ‘could have been interfering with William Skirmish’s mind as well. It could have made him come down West just so he could have his head knocked off. I mean, if it can mess with one person’s mind, why not another, why not yours or mine?’

I remembered the horror of Coopertown’s face as he lurched towards me across the balcony, and the smell of blood. ‘Thank you for that thought, Lesley,’ I said. ‘I shall certainly treasure it for ever – probably late at night when I’m trying to sleep.’

Lesley glanced at where Celia Monroe sat demurely. ‘She had the same kind of sudden mad rage,’ she said. ‘What if her mind had been messed with too?’

‘Her face didn’t fall off,’ I said.

Celia Monroe caught us looking at her and flinched. ‘What if Coopertown was the big splash,’ said Lesley, ‘and she was just an echo? There could have been other incidents going on all over the place, but we just happened to be there when this one blew.’

‘We could check the crime reports and see if anything fits,’ I said. ‘See if there’s a cluster.’