But then the informer had provided an address, and this caused a certain hesitation. The brothel was in one of the better streets of the New Town, quiet Georgian terraces, lined with trees and Saabs and Volvos, the houses filled with professional people: lawyers, surgeons, university professors. This was no seaman's bawdy-house, no series of damp, dark rooms above a dockside pub. This was, as Rebus himself had offered, an Establishment establishment. Watson hadn't seen the joke.

Watch had been kept for several days and nights, courtesy of unmarked cars and unremarkable plainclothes men. Until there could be little doubt: whatever was happening inside the shuttered rooms, it was happening after midnight and it was happening briskly. Interestingly, few of the many men arrived by car. But a watchful detective constable, taking a leak in the dead of night, discovered why. The men were parking their cars in side streets and walking the hundred yards or so to the front door of the four-storey house. Perhaps this was house policy: the slamming of after-hours car doors would arouse suspicion in the street. Or perhaps it was in the visitors' own interests not to leave their cars in broad streetlight, where they might be recognized…

Registration numbers were taken and checked, as were photographs of visitors to the house. The owner of the house itself was traced. He owned half a French vineyard as well as several properties in Edinburgh, and lived in Bordeaux the year through. His solicitor had been responsible for letting the house to a Mrs Croft, a very genteel lady in her fifties. According to the solicitor, she paid her rent promptly and in cash. Was there any problem…?

No problem, he was assured, but if he could keep the conversation to himself.