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 . . .