Twenty years retired from the Intelligence Service, David Cartwright still knows where the skeletons are hidden. But when he forgets that secrets are supposed to stay buried, there’s suddenly a target on his back.

His grandson, River, is a ‘slow horse’, a demoted spy pushing paper at Slough House with other no-hopers. With his grandfather under threat, River ditches desk duty and goes rogue to investigate.

Jackson Lamb, the boss at Slough House, worked with David Cartwright back in the day. He knows better than most that this is no innocent old man. So when River’s panic button raises the alarm at Intelligence Service HQ, Lamb will do whatever he thinks necessary to protect an agent in peril.