'Have you reached any conclusion yourself?' asked Leeming.

'Only the obvious one, Sergeant – it was murder for gain. The victim was killed so that he could be robbed.'

'Oh, I suspect that there was much more to it than that,' said Colbeck. 'A lot of calculation went into this murder. Nobody would take so much trouble simply to get his hands on the contents of another man's wallet. Always reject the obvious, Inspector Heyford. It has a nasty tendency to mislead.'

'Yes, sir,' grunted the other.

Colbeck stood up. 'Let's get started, shall we? Suggest a hotel then lead me to the mortuary. The sooner we get that description in the newspapers, the better. With luck, he may read it.'

'Who?'

'The other witness. I discount the two ladies and the boy. They'll have been too shocked to give a coherent account. But there was a man on that bank as well. He's the person who interests me.'

Ambrose Hooper put the finishing touches to his work then stood back to admire it. He was in his studio, a place of amiable chaos that contained several paintings that had been started then abandoned, and dozens of pencil drawings that had never progressed beyond the stage of a rough sketch. Artist's materials lay everywhere. Light was fading so it was impossible for him to work on but he did not, in any case, need to do so. What he had achieved already had a sense of completeness to it. The sketch he had made of the Sankey Viaduct was now a vivid watercolour that would serve as model for the much bigger work he intended to paint.

It was all there – viaduct, canal, train, sailing barge, lush green fields, cows and, in the foreground, two women and a small boy. What brought the whole scene together, giving it life and definition, was the central figure of the man who was tumbling helplessly through the air towards the water, a bizarre link between viaduct and canal. Hooper was thrilled. Instead of producing yet another landscape, he had created a unique historical document. It would be his masterpiece.