A lone German bomber crosses the east coast of Britain on a moonless night in the long, hot summer of 1940. The pilot picks up the silver thread of a river and, following it to his target, drops his bomb over Cambridge's rail yards. The shell falls short of its mark and lands in a neighbourhood of terraced streets on the edge of the city's medieval centre.DI Eden Brooke is first on the scene and discovers the body of an elderly woman, Nora Wylde, in a house on Elm Street, two fingers on her left hand severed, in what looks like a brutal attempt by looters to steal her rings.When the next day Nora's teenage granddaughter Peggy, a munitions worker, is reported missing, Brooke realises there is more to the situation than meets the eye.