David Cartwright has left his library to the Spooks’ College in Oxford, and now one of the books is missing. Or perhaps it never existed. River, once a “slow horse” of Slough House, MI5’s outpost for demoted and disgraced spies, starts investigating the secrets of his grandfather’s library. Over at the Park, MI5 First Desk Diana Taverner is in a pickle. An operation carried out during the height of the Troubles laid bare the ugly side of state security, and those involved are threatening to expose details. But every threat hides an opportunity, and Taverner has come up with a scheme. Jackson Lamb, the enigmatic and odiferous head of Slough House, has no plans to send in the clowns. On the other hand, if the clowns ignore his instructions, any harm that befalls them is hardly his fault. But they’re his clowns. And if they don’t all make it home, there will be a reckoning.