1860, Wimborne, Dorset. Rebecca Tullidge, miserably married to her callous husband, finds some escape through a love affair with another man. After putting her drunk husband to bed one Saturday night, she sneaks from their lodge to meet railway officer, John Bedloe. But much to her horror, she trips over her lover's corpse on the railway tracks.

The railway director calls Inspector Colbeck and Sergeant Lemming in from London to solve the hideous crime. As the pair arrive in the countryside, they find there is no shortage of difficult personalities and conflicting alibis, making the mystery much harder to unravel.

On discovering Bedloe had plenty of enemies as well as a sordid past, Colbeck and Leeming must unearth which of them is capable of plotting a violent murder. Could it possibly be a woman, distraught that he'd taken another lover? Or a jealous husband who detected an affair? With pressure mounting from all sides, the Railway Detective is tasked with uncovering the truth.