‘Maybe. It seems quite violent, and I suppose people only do that if they either want something to really hurt or to send a message. Backtrack for me, though . . . you’re saying this is ash, but the snow wasn’t melted. This killer sets them on fire without setting them on fire?’

‘It’s an ancient torture technique once used by Persian kings, actually,’ Sofia said from the doorway. ‘What? I was freezing my arse off.’

‘Torture?’ I raised an eyebrow at Erin. ‘Fits with sending a message.’

‘How much does she know?’ Erin folded her arms. ‘Michael told me to only trust you.’

‘She’s okay. She knows about the money.’

‘It’s too bad Ern’s already spent’—Sofia shot me a sly glance—‘a fair chunk of it. At least fifty kay, right?’

Erin fixed me with a look that I couldn’t decipher. It was either annoyance that I’d spent Michael’s money, or that I’d become close enough to Sofia to tell her my secrets. I settled on the second, thinking it was a bit rich from someone who’d spent last night with my brother. ‘You seem to know an awful lot about this serial killer,’ Erin said, still wary.

If Sofia thought she was being accused, she didn’t show it. ‘We had a victim through one of our hospitals. The Humphreys woman. Someone found her, and everyone thought they’d got her just in time. But her lungs were shot – we had to switch the ventilators off. I found it interesting, listened to a few podcasts. Didn’t really think I’d need the information until, well, ever. But here we are.’

‘Well, close the case. If you listened to a podcast . . .’

‘Give her a chance, Erin. She knows more than we do.’

‘So we’re looking for a history buff? With a taste for medieval torture?’

‘Kind of.’ Sofia looked embarrassed. ‘I didn’t make this up, okay? It’s called suffocation by ash. Ernie, I told you before that most people who die in house fires don’t burn to death, they asphyxiate. That’s partly because fire pulls oxygen out of the air, so there’s nothing to breathe, but even after the fire is out, if you breathe in too much smoke it can coat your lungs so that you couldn’t get oxygen out of the air even if it were there.’

‘And ancient Persia is known for its house fires?’ I asked.