It is 1941 and the Germans have won the Battle of Britain. Detective Douglas Archer finds himself working under the brutal SS in occupied London. Archer investigates the murder of a black marketeer. When the glamorous US journalist Barbara Barga is spotted at the scene of the crime, Archer's gut feeling that this crime is far bigger than it would at first seem is confirmed, and he soon finds himself embroiled in a deadly plot.

Finding the missing atomic bomb documents becomes Archer's main priority as he frantically tries to track down the elusive Dr John Spode. Still a target for the Resistance, Archer faces a fatal tussle on the underground and a deadly explosion at Highgate Cemetery.

With the army imposing martial law and a rounding-up of Resistance members, Archer faces life-changing decisions. Barbara's surprise proposal could provide a safe haven for Archer and his son, but can he really trust her with the country's most sought-after possession? Despite being caught in the middle of a battle between Kellermann and Huth, will Archer finally agree to help free the King?

Archer and Harry attempt to drive the king out of London, but things do not go to plan and Sylvia becomes an unlikely ally. Following a rough interrogation with a badly shaken Barbara Barga, Kellermann is hot on Archer's heels.