This is the 5th novel in the 'Quest' series of mystery / thrillers set in the world of the 1950s.
'A Quest in Berlin' plunges Andrew and Clemency into peril as they arrive in a city that still bears the scars of war and is now at the centre of the Cold War. It's a place and a situation in which they don't know who to trust.
An old friend and colleague appears in Andrew's life and persuades him to travel to Berlin with her to help with a personal crisis. Clemency certainly isn't supposed to follow them into danger, but of course she can't resist it, despite dire warnings of the dangers involved from others in the family.