Just over ten minutes later I reach the building. Despite the early hour the heavy thump of bass is audible way down the street. The guy on the door – black jeans, black shirt, a curl of white snaking out of his ear – stops me.

‘No dogs allowed.’

‘Ron Koopmans in?’

The guy’s neck is almost as thick as his head, which is shiny-bald.

‘Who wants to know?’

‘Jaap Rykel.’ He stares at me. ‘Inspector Jaap Rykel,’ I clarify after a few more moments.

He looks me up and down once before raising his arm and talking to his cuff.

A few minutes later Ron steps out through a fire door further down the building, and waves me over whilst he holds it open. He’s a good head shorter than me, allowing me to see he’s starting to thin on top. As if to make up for it he’s wearing a beard, which I’m sure he never used to.

‘Jaap, how are you? Long time no see.’

‘Yeah, good.’

He looks at me as if he can see the lie, but doesn’t comment. ‘Come in.’

‘What about him?’ I point to Kush. ‘Your guy said no dogs.’

Ron gives him the once-over, then shrugs. ‘Frankly he looks more civilized than most of the customers here. Anyway, I’m head of security. Shall we?’

We catch up whilst he takes me through a series of corridors to his office, a room with a massive bank of computer screens covering just about every angle in the club’s multiple rooms. A woman with spiky dyed-blonde hair and large hooped earrings sits in front of them.

‘So, what can I do for you? Assuming this wasn’t all social.’

I tell him about the report of a Jan Akkerman caught groping a woman.

‘Honestly, it’s not that rare an occurrence sadly. When did you say it was?’

‘Twentieth of February.’

‘Claudia, you remember that?’

Claudia turns to look at us. She’s older than I assumed from the hairstyle; she must be well into her fifties.

‘So many creeps,’ she says. ‘What was that date again?’

Ron tells her.

‘You can look it up in the dailies then,’ and she turns back to the bank of screens.

For some reason I get the sense there’s something between these two. More power struggle than anything romantic, though. Ron rolls his eyes, sighs, mutters something about doing stuff yourself being the only way to make sure it’s done right, and opens a laptop. As it’s booting up he points to one of the screens on the bank, a bird’s-eye view of one of the largest rooms in the club. The wall is made entirely of glass, opening onto a view of the IJ’s waters. I realize I could probably see Nellie’s house across the water if I were to go and stand in the room and look north.