London's Slough House is where the washed-up MI5 spies go to while away what's left of their failed careers. The 'slow-horses', as they're called, have all disgraced themselves. Some messed up an op badly and can't be trusted anymore. Others got in the way of an ambitious colleague and had the rug pulled from under their feet. Maybe they just got too dependent on the bottle. All have one thing in common: they all want to be back in the action and they'll do anything to get there, even if it means actually cooperating.