An Instant Sunday Times Bestseller and a gripping standalone thriller with a riveting reveal about a disastrous MI5 mission in Cold War Berlin. A dazzling entry-point to Mick Herron's writing and an unmissable read for Slough House fans.

Two years ago, the Monochrome inquiry was set up to investigate the British secret service. Monochrome's mission was to ferret out misconduct, allowing the civil servants seconded to the inquiry, Griselda Fleet and Malcolm Kyle, unfettered access to confidential information in the service archives.

But with progress blocked at every turn, Monochrome is circling the drain . . . Until the OTIS file appears out of nowhere.

What classified secrets does OTIS 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?

Spies and pen-pushers, politicians and PAs, high-flyers, time-servers and burn-outs . . . They all have jobs to do in the daylight. But what they do in the secret hours reveals who they really are.