River Cartwright is ousted from MI5 and finds himself in a place worse than purgatory: Slough House, dumping ground for failed spies.

River and Sid join forces. A misfired gun has dire consequences.

Slough House is the unlikely venue for a secret romance, but events take a dark turn when a dangerous encounter becomes deadly.

The Slow Horses must disappear to avoid capture by MI5. Lamb and River head to The Park to outwit Taverner.