That night he dreamed in Technicolor. He saw the ochre-skinned, scantily clad siren in her black, arrowed stockings. And in Morse’s muddled computer of a mind, that siren took the name of one Joanna Franks . . .

The body of Joanna Franks was found at Duke’s Cut on the Oxford Canal at about 5.30 a.m. on Wednesday, 22nd June 1859.

At around 10.15 a.m. on a Saturday morning in 1989 the body of Chief Inspector Morse – though very much alive – was removed to Oxford’s John Radcliffe Hospital. Treatment for a perforated ulcer was later pronounced successful.

As Morse begins his recovery he comes across an account of the investigation and the trial that followed Joanna Franks’ death . . . and becomes convinced that the two men hanged for her murder were innocent . . .