Meg Elginbrodde, a young war widow, receives photographs that suggest her husband is still alive so she enlists the help of her cousin, Albert Campion to investigate. The man in the photographs turns out to be a known felon, ‘Duds’ Morrison. Meg’s jealous fiancé, Geoffrey Levitt, accosts Duds but both men are attacked by a criminal gang posing as a rackety street band. Meanwhile, Meg’s father, Canon Avril, a gentle priest, wonders how Duds came to be wearing Meg’s husband’s coat. A tortuous trail leads through the oppressive London fog to Jack Havoc, a violent murderer. Set in a dingy and damaged post war London this is Allingham’s most sophisticated novel which examines the very nature of evil.