In 1941, after a telephone tip off to the Assistant Commissioner of the Metropolitan police the body of a young woman, Sarah Davis is discovered during the hours of the Blackout and at the height of a bombing raid by two Scotland Yard Detectives. The murder victim as reported to the Yard was found on the floor of the master bedroom in a rather rundown South London terraced house in a side street off the Kennington Road. This was a swift, clinical killing, and a single bullet wound to the forehead had killed Sarah Davis instantly. With the nightly Blackout crime was easy to conceal, the house was already damaged by a bomb blast; a direct hit would have obliterated any chance of finding forensic evidence. If they hadn't reached the body, the auxiliary services would simply have pulled Sarah's mutilated body out of the rubble without a second thought, and assumed she died as a result of the bombing. As Chief Inspector Luke Garvan knelt over the body illuminated by the weirdly intense bluish light of the incendry bombs exploding along Monkton Drive, he felt that this was no ordinary murder; it had all the hallmarks of a professional killing. On returning to the crime scene the following day his suspicions were confirmed when he found the leading Home Office Pathologist Sam Menzies examining the body rather the local Police Surgeon. Back at Scotland Yard during a meeting with the Assistant Commissioner he is introduced to Spencer Hall who claims to be from The Home Office, he is in fact like Sarah Davis a member of MI5's shadowy Twenty Committee. In normal circumstances Special Branch would have taken the lead on an investigation involving the security services, but for some reason MI5 demanded that Garvan head up the inquiry. Garvan's initial instinct that the murder had all the hallmarks of a professional killing are confirmed when Spencer Hall explains that MI5 believe Sarah was killed by one of their double-agents on the direct order of German Intelligence, and that as a consequence the Twenty Committee is on the brink of disaster. Their work is vital for the future conduct of the War; and one rogue agent could bring the entire system crashing down like a pack of cards. The price and the stakes are high; the Investigation becomes a race against time to track down the killer of Sarah Davis before it's too late, and Britain's counter-espionage battle against the Abwehr is lost, and the result, could quite literally affect the final outcome of the War against Nazi Germany