‘I’m just quickly going to throw something more comfortable on to wear. I won’t be a second, there’s wine in the fridge, help yourself. I took the liberty of making up the spare room for you, unless you’ve booked a hotel? I can always call you a cab,’ Kelly said.

‘Thanks, I’m booked into a Premier Inn on some motorway junction. It’ll do, but thanks for the invite. Next time. I could murder a glass of wine.’

Kelly went upstairs and peeled off her detective uniform: when she wore it, she called it her ‘plain clothes shuffle’. She pulled on some jeans and a thin sweater, checked her make-up and slipped on some pumps. When she went back downstairs, Demi had made herself comfortable under one of the blankets on a lounger outside on the terrace. Kelly poured a glass of well-chilled white wine and joined her.

‘You know Rob’s app – DC Shawcross – he made the pentacle app so we could impose it onto a map at any scale? Yes, well I reckon the seasons have something to do with the killings as well. The two animal cruelty cases were at the start of a spring festival Pagans call Imbolc, and the disappearance of the two boys happened much later in the year during the festival of Samhain. That’s the death of the year, and it kicks off with Halloween. Now, before you go all spooked on me, Halloween isn’t anywhere near as old as things like the Day of the Dead – which is essentially the same thing – the death of the year, and treating the dead with respect has happened for centuries. The Christian version is much more recent.’

‘I’m not spooked at all. I was in Mexico three years ago for the Day of the Dead, it’s a fabulous experience if you ever get the chance. You say these crimes are connected, and if that’s correct, then it means that over the course of the last, what? Twelve years? They’ve been happening subtly – carefully even – not brazen or exhibitionist at all, so why now? It’s a change of profile, a change of MO. It doesn’t fit. Sure, you have escalation, but the finality of what’s going on, the public nature of the crimes, is unexpected, given the rest of the information we know.’

‘I know.’

‘Different perps? An accomplice branching out on their own? An apprentice finally ready?’

‘It’s all plausible. That’s what I find so frustrating. There are so many potential outcomes for this case, and at the moment, catching the bastard isn’t one of them.’

‘Or bastards.’

‘No. It’s a lone operator. I’ve seen it before.’

‘The Teacher?’