The secret hours by Mick Herron

Monochrome is a busted flush. Beginning as an investigation into the historical misdeeds of the intelligence services by a vindicative prime minister, Monochrome is now circling the drain, much like the careers of the two civil servants – Griselda Fleet and Malcolm Kyle – charged with overseeing the inquiry. And then the OTIS file falls into their hands. What secrets does this hold that see a long-redundant spy being chased through Devon’s green lanes in the dark? What happened in a newly reunified Berlin that someone is desperate to keep under wraps? And who will win the battle for the soul of the secret service – or was that decided a long time ago?