So they walked across the car park to the cafeteria, with its piped music and the smell of baking bread pumped specially from the kitchen to make the place appear welcoming. Then they sat at a quiet table gossiping, more like mother and daughter than like strangers.

Claire Bingham’s loss of nerve on the M5 was to prove a turning point in the case, though they never discussed it again. There were no longer two separate and parallel investigations. She found herself prepared to listen to Molly’s ideas and trust her judgement. By the time they had the conference with George in the hospital, she was open to his theory that Duncan James had been blackmailed by Greg Franks over the Rashwood development. She listened carefully to the views of Molly and George and found they had quite different ideas about how the case would be resolved. With the experience on the motorway, her hero worship had returned. She was prepared to consider a flexibility in her methods which would have astounded her colleagues at Heanor, who saw her as a mindless follower of rules.

It was Claire who charmed and wheedled information and reminiscences from the retired policeman who had looked into the fire at Sinclair’s boat yard. It was Claire who came up with the ultimate coincidence.

She went first to the police station in the city centre where Rosco had been charged with arson and manslaughter. A middle-aged detective constable was waiting for her, but she soon gathered that Wargan, who had arranged the visit by phone, had not described it as of any urgency or importance.

“Just background you wanted, according to your superintendent,” the D.C. said, pulling a chair for her up to his cluttered desk. “There won’t be many people working here who remember the case now. Everything’s changed.”

“What have you got in the way of background?” she asked, and he brought out a few tatty pieces of paper, case notes, photocopies of which she had already seen.

“Is that all?” she said. “ There must be something else. Someone who remembers the Rosco case. It was a big fire. It must have stuck in people’s memories.”

And because she was attractive and smiled at him, he made coffee for them both and talked to her. He told her about Hubert Rolfe, the detective sergeant who had never believed Rosco had planned the fire by himself, and who had made such a nuisance of himself about the case that he was forced to take early retirement.

“Not a popular man, Hubert Rolfe,” the detective said. “ Not here.” He looked around him to check that no one was listening. “Too straight sometimes for his own good. He’s a great one for causes. Now he’s got a bee in his bonnet about the development of the docks. Says it’s changed the character of the city. You often see letters from him in the paper.”