Helen had been talking about school, telling Cooper about the children in her class. Cooper had been content to listen to her talk. He had come intending to make amends for standing her up at the rugby club the previous Sunday. He knew he had been neglecting her. Yet the lack of necessity for a response allowed his thoughts to drift occasionally. His mind kept returning to the reports of the attack on Cal and Stride in the quarry the previous night. The details had been shocking in themselves; but his imagination was able to provide much worse. Cal and Stride were the typical victims – a pair of innocents who had found themselves in the wrong place at the wrong time. He had seen what they were, and he had been unable to do anything to protect them.

And now Cooper had something else on his mind. He had to decide what to do about Mark Roper and Owen Fox. Mark’s suspicions were insubstantial, yet Cooper would have to report them. Perversely, he felt he would have liked to be able to discuss the subject with Diane Fry. He would also have liked to have been part of the team that was trying to identify the vigilante group which had attacked her. They had the reports from Fry and PC Taylor, and Cal and Stride themselves were being interviewed. But the scene was a mess – the rain had left it a quagmire. An assault on a police officer had to be treated seriously, but all that had been achieved so far was to spread the division’s resources even thinner. It was enough to make Cooper feel guilty about taking time off. But there was no more money in the budget for overtime.

Helen dipped into her shoulder bag and produced a packet of photos. Cooper looked at them, puzzled.

‘The pictures of the children,’ she said.

‘Oh, right.’

On Sundays, the riverside was always busy with families feeding the ducks. From the river walk, the water seemed to be full of movement. Mallards and coot clustered anxiously round the bankside, darting for the tidbits. Flocks of black-headed gulls wheeled and screamed over the surface, landing and taking off again, noisy and bad-tempered.

They sat down on a bench next to an elderly couple. The photos were all badly composed and had a strange cast over them, a combination of artificial light and direct flash.

‘This is my little favourite, Carly,’ said Helen, pointing to a little girl of about six, with fair hair cut raggedly across her forehead and a selection of teeth and gaps like a half-demolished wall.

‘She’s really sweet. She likes to draw, and she insists on giving me her drawings as presents. Look at this.’