He frowned at this, looking from the river to the bridge to the great puffs of fog rising like a gas from the fen. As the subject for a painting, it reminded him of that French stuff he’d seen at the Courtauld Institute years ago, dots and swirls and dashes of colour that you could only fi gure out if you stood forty feet away and squinted like the devil and thought about how things might look if you needed specs.

Further along, the planks veered to the left, and he came upon his police photographer and the forensic biologist. They were bundled against the cold in overcoats and knitted caps, and they pranced about like two Russian dancers, hopping from foot to foot to keep the circulation going. The photographer looked as pale as he usually did prior to having to document a killing. The forensic biologist looked peeved. She hugged her arms to her chest, shifted from one foot to the other in a bobbling fashion, and glanced repeatedly and restlessly in the direction of the causeway as if in the belief that the killer lingered beyond them in the fog and only by plunging through it immediately could they hope to apprehend him.

As Sheehan reached them and began to ask his customary question-“What d’we have this time?”-he saw the reason for the forensic biologist’s impatience. A tall fi gure was emerging from the mist beneath the crack willows, walking carefully with his eyes on the ground. In spite of the cold, his cashmere greatcoat was slung indifferently round his shoulders like a cape, and he wore no scarf to detract from the crisp, clean lines of his Italian suit. Drake, the head of Sheehan’s forensic department, one-half of a bickering duo of scientists that had been aggravating him for the last fi ve months. He was indulging in his flair for costume this morning, Sheehan noted.