Detective Chief Inspector Endeavour Morse and Chief Superintendent Jim Strange (James Grout) attend an exhibit entitled "Criminal Oxford: Crime and Punishment in Victorian Times" (Colin Dexter is in attendance). During a lecture by Dr. Millicent Van Buren (Lisa Eichhorn), a visiting professor from Boston University, Morse starts to feel ill. After the lecture Dr. Van Buren wants to speak at length with Morse, but he feels worse, excuses himself, and then passes out in the lavatory, to be found by Strange on the floor grasping his stomach.
While hospitalized he is diagnosed with a bleeding ulcer, which his doctor ascribes mainly to Morse's excess consumption of alcohol. To pass the time in his recovery he reads the book by Van Buren entitled "Criminal Detection in the Victorian Period", about the 1859 "Oxford Canal Murder", and becomes convinced that a miscarriage of justice occurred in the trial that followed, Victoria Regina v. J Oldfield and Others.
In 1859 the body of a woman is found floating in the Oxford Canal. A man, later identified as Donald Favant, who had stayed the previous night at The Bear, an inn at Woodstock, was seen walking along the river bank (or tow path) away from where the body was found. The body of the woman was presumed to be that of Joanna Franks (Juliet Cowan) who was taking the fly boat (canal barge) the Barbara Bray owned by the canal boat company J. & M. Pickford & Co., from Coventry to London to join her husband Charles.
Three boatmen, crew of the Barbara Brey, Rory Oldfield, Alfred Musson, and Walter Towns, are accused of the murder of the woman, who was positively identified by her husband. Two of the boatmen are hanged. But Morse does not believe that they were the perpetrators.
Joanna had previously been married to a music-hall entertainer, "The Great Donavan, Emperor of all illusionists." Donavan had died in Ireland, so she remarried Franks, who went on ahead to London for work and then when he had saved up enough had sent for her.
With the assistance of Adele Cecil (Judy Loe), who was introduced in the previous episode, and Police Constable Adrian Kershaw (Matthew Finney), Morse uncovers several inconsistencies in the trial and suspects insurance fraud. She could have paid six shillings for a third-class rail ticket, and been there a lot faster, instead of the four shillings she paid for the fly-boat. She accused the boatmen of being rude and drunk, but then right after her complaint to the canal clerk, she was seen drinking and smiling with them. Thomas Wootton, a 15-year old and the fourth boatman for the Barbara Brey, was not charged, but testified for the prosecution. The size of Joanna's shoes don't seem to fit with her dress, which had been altered. Her knickers, which had been described as torn or ripped, where actually cut with a knife deliberately.
Although he is unable to exhume the body of Joanna Franks, Morse travels to Bertraghboy Bay, on the west coast of Ireland to open the grave of Frank Donovan. Morse figures out that Donald "Don" Favant and Charles Franks are aliases derived from Frank "F. T." Donavan. The grave is empty.
Detective Sergeant Robert Lewis does not appear in this episode because he is out of town on an inspector's course.