Fatherland

Fatherland - Robert Harris Set in 1964 in a world where Germany won the war (although Russia still holds out against them), a series of events drag detective Xavier March into an investigation loaded with danger.
As he picks his ways through the clues, the atmosphere gets more and more tense as he has to watch his every step.

The whole novel has a sense of suspicion around every character and event, in the backdrop of a grimy Berlin getting ready to celebrate Hitler's birthday.