They left their cars and vans and marched towards the front door. Knocked quietly. The door was opened from within, and then things began to move like a video on double-speed. Other doors were opened . . . how many doors could a house have? Knock first, then open. Yes, they were being courteous.

‘If you wouldn’t mind getting dressed, please . . .’

‘If you could just come downstairs now . . .’

‘You can put your trousers on first, sir, if you like . . .’

Then: ‘Christ, sir, come and take a look at this.’ Rebus followed the flushed, youthful face of the detective constable. ‘Here we are, sir. Feast your peepers on this lot.’

Ah yes, the punishment room. Chains and thongs and whips. A couple of full-length mirrors, a wardrobe full of gear.

‘There’s more leather here than in a bloody milking shed.’

‘You seem to know a lot about cows, son,’ Rebus said. He was just thankful the room wasn’t in use. But there were more surprises to come.

In parts, the house resembled nothing more lewd than a fancy-dress party – nurses and matrons, wimples and high heels. Except that most of the costumes revealed more than they hid. One young woman seemed to be wearing a rubber diving suit with the nipples and crotch cut away. Another looked like a cross between Heidi and Eva Braun. Watson watched the parade, righteous fury filling him. He had no doubts now: it was absolutely proper that this sort of place be closed down. Then he turned back to the conversation he was having with Mrs Croft, while Chief Inspector Lauderdale lingered only a short distance away. He had insisted on coming along, knowing his superior and fearing some almighty cock-up. Well, thought Rebus with a smile, no cock-ups in sight yet.

Mrs Croft spoke in a kind of gentrified Cockney, which became less gentrified as time went on and more couples spilled down the stairs and into the large, sofa-crammed living room. A room smelling of expensive perfume and proprietary whisky. Mrs Croft was denying everything. She was even denying that they were standing in a brothel at all.

I am not my brothel’s keeper, thought Rebus. All the same, he had to admire her performance. She was a businesswoman, she kept saying, a taxpayer, she had rights . . . and where was her solicitor?

‘I thought it was her that was doing the soliciting,’ Lauderdale muttered to Rebus: a rare moment of humour from one of the dourest buggers Rebus had ever worked with. And as such, it deserved a smile.

‘What are you grinning at? I didn’t know there was an interval. Get back to work.’

‘Yes, sir.’ Rebus waited till Lauderdale had turned away from him, the better to hear what Watson was saying, and then flicked a quick v-sign at him. Mrs Croft, though, caught the gesture and, perhaps thinking it intended at her, returned it. Lauderdale and Watson both turned towards where Rebus was standing, but by then he was already on his way . . .