We drive in silence for a minute. The radio burbles quietly over the humming of tyres on blacktop.

‘How did you go with the local cops who worked the other disappearances?’ I ask.

‘Mixed. Some of them went straight into ass-covering mode—they should have connected these disappearances earlier. Others didn’t want an FBI agent and an algorithm telling them how to do their jobs. A few were openly hostile. All of them shared their case files in the end, so we have a lot to work with. But I’m not convinced any of it will be useful.’

‘Because the cops didn’t seem competent?’

‘Because it’s a serial killer. The files mostly looked at suspects the victims knew well, and their potential motives. Serial killers often target strangers, and their motives can be incoherent.’ She honks at a slow-moving BMW in front of us. ‘Fortunately for us, they also tend to have low IQ.’

This is a misleading statistic. Psychologists only test the ones who get caught. I watch snowflakes land on the windshield, and get swept away by the wipers.

‘What did you say?’ Thistle asks.

‘I didn’t say anything.’

‘Something about a misleading statistic?’

I hadn’t realised I was talking aloud. How often do I do that?

‘They only test the ones they catch,’ I say. ‘The world could be full of serial killers who are too smart to get arrested.’

‘Yeah, well, let’s hope it’s not. Hypothesis—Biggs found out Luxford had raped his daughter. He confronted Luxford, who killed him to keep the secret.’

‘Why wouldn’t Biggs just go to the cops?’

‘If my dad found out that I’d been raped, he wouldn’t have gone to the cops. He would’ve just shot the motherfucker. Hell, he sometimes threatened to do that even when I consented.’

I remember Bob, the big man who nearly adopted me. The landscaper.

‘Your dad wasn’t a math professor,’ I say.

‘You think math professors don’t shoot people?’

‘Statistically, violent criminals don’t have that level of education.’

‘Well, look who’s pro-college all of a sudden,’ Thistle says. ‘And remember what you said a minute ago about serial killers. Anyway, maybe he didn’t go to the cops for the same reason his daughter didn’t. No proof. Fear of humiliating her.’

I nod slowly. ‘Possible,’ I say. ‘Like I said, Luxford’s a sociopath. He wouldn’t think twice about killing Biggs to save his own skin.’

‘He could have been blackmailing Biggs at the same time,’ Thistle says. ‘Hence the cash Biggs took out of the ATM.’

‘Why kill him, then?’

Thistle chews her lip. I try not to remember how good those lips tasted. We kissed four times, and I remember them all vividly.