'A decent, hardworking chap, with not an enemy anywhere. People were surprised that anybody should want to kill Jim.'

But Jim has been found stabbed in the back near Ely, miles from his Yorkshire home. His body, clearly dumped in the usually silent ('dumb') river, has been discovered before the killer intended-disturbed by a torrential flood in the night.

Roused from a comfortable night's sleep, Superintendent Littlejohn of Scotland Yard is soon at the scene. With any clues to the culprit's identity swept away with the surging water, Bellairs's veteran sleuth boards a train heading north to dredge up the truth of the real Jim Teasdale and to trace the mystery of this unassuming victim's murder to its source.