London, October 1941. Freddie Hackett, a message runner for a government office, witnesses an argument that ends in murder. Dismissed by the police when reporting the crime, Freddie turns to private investigator Maisie Dobbs for help.

While Maisie believes the boy and wants to help, she must exercise caution given her work with a secret government department spearheading covert operations against the Nazis. When she stumbles upon the killer in a place she least expects, Maisie soon realises she's been pulled into the orbit of a man who has his own reasons to kill - reasons that go back to another war.