‘Why not keep using the dark web?’ I ask.

‘Because the cops might notice. We can’t see what people are doing on the dark web, but we can tell they’re on it. Whereas a USB stick in the mail isn’t too suspicious. It might get X-rayed, but not read. We did find a USB stick, but it’s encrypted too.’

I stare at the post-it note, still stuck to the computer. MTEDUFIHCRPFO. Impossible to remember, unless you’ve had plenty of practice memorising random letters. Easier to just write it down, like he did. But what for, if it’s not the password?

‘Bring up the login screen,’ I say.

Vasquez does. ‘We can’t just guess,’ he said. ‘After two more wrong attempts, the hard drive will erase itself.’

Thirteen letters. I close my eyes and think back to the wheel cipher on Luxford’s desk, back at the college. Thirteen discs. The configuration meaningless.

‘What do you have in mind?’ Thistle asks me.

‘Hang on.’ I didn’t have time to memorise the order of the letters on every disc, and I only saw the wheel cipher from one side. But I think I have just enough. In my head, I rotate the discs, lining up the letters from the post-it note: MTEDUFIHCRPFO.

And there it is, on the row just above. A message in plain English.

I open my eyes. ‘Try show me the pain,’ I tell Vasquez. ‘All one word.’

‘You’re sure?’

‘I’m sure.’ I look at Thistle. ‘He used his wheel cipher. The thing on his desk.’

Thistle squeezes my shoulder as Vasquez types it in.

A message pops up: Incorrect password. One attempt remaining.

‘Shit,’ Thistle says. ‘Sorry, Blake.’

‘Was that upper case, or lower case?’ I ask Vasquez.

‘Lower case.’

‘Try upper.’ All the letters on the cipher were capitals.

‘Really? If you’re wrong, we lose everything.’

‘Do it,’ I say.

Vasquez looks at Thistle for confirmation. She nods. He genuflects and turns back to the keyboard. Types it in.

I hold my breath.

He hits Enter.

Welcome, Shannon!

‘Mother of God,’ Vasquez says.

‘Ha!’ Thistle slaps me on the back, grinning. ‘You did it!’

I exhale, my hands shaking. It feels good to show off in front of Thistle. ‘What’s in there?’

Vasquez is bringing up a file directory. There are hundreds of videos. He hesitates before clicking the first one.

‘What?’ I ask.

‘A guy with an encrypted hard drive, a Tor browser and “show me the pain” as his password probably has some pretty bad videos in his collection,’ Vasquez says.

‘No shit,’ Thistle says. ‘You remember we found a young woman being held prisoner in his house?’

‘I’m just saying, whatever this is, maybe you don’t want to see it.’

The excitement has faded from Thistle’s face. ‘We have to.’