Zen held his identity card up to the camera above the bell and the door release hummed loudly. Since the years of terrorism, police stations had been defended like colonial outposts in enemy territory. The fact that the Questura and the Squadra Mobile headquarters next door were both traditional buildings typical of this unglamorous area of the city made such measures seem all the more bizarre.

The guard on duty behind a screen of armoured glass in the vestibule was sleepy and offhand. No one was in yet, he told Zen, a claim substantiated by the bank of video screens behind him, showing a selection of empty rooms, corridors and staircases. Zen walked upstairs to the first floor and opened a door at random. The scene which met his eyes inside was absolutely predictable to anyone who had worked in police offices anywhere in Italy from Aosta to Siracuse. The air was stale and stuffy, used up and warmed over. The bare walls were painted a shade of off-white reminiscent of milk left too long out of the fridge. A double neon tube housing, its cover missing, hung from the ceiling on frail chains. The available space was divided into three areas by screens of the thick frosted glass commonly associated with shower cubicles, set in gilt-anodized aluminium frames. At the centre of each squatted a large wooden desk.

Zen went over to one of the desks and looked through the contents of the three-tiered metal tray until he found what he was looking for: a sheaf of computer printout stapled together at the upper left-hand corner. The top sheet bore the words NOTIZIE DI REATI DENUNCIATI ALLA POLIZIA GIUDIZIARIA and the dates of the previous week. The pages inside listed all the incidents which had been brought to the attention of the police during the period in question. Zen leafed through the pages, looking for something suitable.

It was a delicate business. He didn’t want to attract unwanted attention by poaching a case which had already been assigned, or in which someone was taking a special interest for one reason or another.