When a young man is kidnapped and threatened with beheading, the slow horses find themselves unexpectedly embroiled in a dangerous case that forces them to prove their worth.

Long-buried Cold War secrets emerge which threaten to bring carnage to the streets of London. When a liaison with Russian villains takes a fatal turn, our hapless heroes must overcome their individual failings and raise their spy game in a race to prevent a catastrophic incident.

A romantic liaison in Istanbul threatens to expose a buried MI5 secret in London. When Jackson Lamb and his team of misfits are dragged into the fight, they find themselves caught in a conspiracy that threatens the future not just of Slough House but of MI5 itself.

In season 4, a bombing detonates personal secrets, rocking Slough House's already unstable foundations.

In season five, everyone is suspicious when resident tech nerd Roddy Ho has a glamorous new girlfriend. When a series of increasingly bizarre events occur across the city, it falls to the Slow Horses to work out how everything is connected. After all, Lamb knows that in the world of espionage, the London Rules — cover your back — always apply.