The bad spies of MI5's Slough House are caught in a deadly battle between MI5's secret past and its murky future in this gripping, hilarious, and heartbreaking new thriller by Mick Herron, "the le Carré of the future" (BBC).

"Old spies grow ridiculous, River. Old spies aren't much better than clowns." Or so David Cartwright, the late retired head of MI5, used to tell his grandson. He forgot to add that old spies can be dangerous, too, especially if they've fallen on hard times--as River Cartwright is about to learn the hard way.

David Cartwright, long buried, has left his library to the Spooks' College in Oxford, and now it turns out that one of the books has gone missing. Or perhaps it never existed . . . Now River, once a "slow horse" of Slough House, MI5's outpost for demoted and disgraced spies, has some time to kill while waiting medical clearance to return to work, and investigating the secrets of his grandfather's library seems a harmless activity. But nothing involving the slow horses ever stays harmless for long.

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 in which the would-be blackmailer is a solution to a much newer problem. All she needs is the right dupe to get caught holding the bag.

Jackson Lamb, the enigmatic and odiferous head of Slough House, does not want any of his joes involved. When Taverner starts plotting mischief people get hurt, and Lamb 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 come home, there'll be a reckoning.