London, September 1941. Freddie Hackett, a message runner for a government office, witnesses an argument that ends in murder. Hiding in the doorway of a bombed-out house, Freddie waits until the coast is clear. But when he arrives at his next delivery address, he's shocked to come face-to-face with the killer. Dismissed by the police when reporting the crime, Freddie turns to private investigator Maisie Dobbs. While Maisie believes the boy and wants to help, she must exercise caution given her work with the French resistance. When she spots the killer in a place she least expects, she soon realises she's been pulled into the orbit of a man who has his own reasons to kill - reasons that go back to the last war.