SS-GB by Len Deighton

The Second World War is over. Germany have won the battle. But the fight goes on...

It is November 1941, nine months after the Nazis successfully invaded Britain. Churchill has been executed and the King imprisoned in the Tower of London. At Scotland Yard, renowned Detective Inspector Archer just tries to keep his head down. But when what seems a routine murder in a Mayfair flat leads him to something far deadlier, Archer becomes caught between his brutal superiors and the British resistance, and drawn into a plot that could change the future of the world.