March, 1918. The Great War is grinding slowly to its bloody finale. Divisional Detective Inspector Ernest Hardcastle, head of the Whitehall Division of the Metropolitan Police, is called to a body is recovered from the Thames. Mavis Parker, the victim’s attractive widow, proves to be a good-time girl, and to complicate matters, all the suspects seem to be known to each other, including a South African who purports to be an actor. But it is when Special Branch intervene that things really get complicated . . .