The Secret Hours

“Slough House” series author Herron (Bad Actors) continues his winning streak with this excellent stand-alone spy thriller. As with previous “Slough House” books, underlings are manipulated like game pieces by their MI5 bosses. Some will rise to the occasion and some will not, and nobody is quite what they seem—to the delight of readers who will enjoy connecting events of parallel stories. In the present, civil servants Malcolm Kyle and Griselda Fleet are assigned to Monochrome, an inquiry looking into “historical overreaching” by MI5 agents. They’re hamstrung from the start by MI5’s top spy, known as First Desk, who blocks all their attempts to get documentation and looks forward to Monochrome’s imminent disbanding due to another political changing of the guard. But on the last day of the inquiry, Fleet and Kyle receive a top-secret file concerning a horribly botched case in 1994 Berlin. Readers are whisked into that story, which features wide-eyed newbie Alison, sent to the divided city to spy on agents working there.