The second series, Dead Lions , premiered on 2 December In June , the programme was renewed for a third and fourth series. The third series, Real Tigers , premiered on 29 November The fourth series, Spook Street , premiered on 4 September In January , it was renewed for a fifth series, which will be based on the fifth book in the series, London Rules. In October , ahead of the fourth series premiere, it was renewed for a sixth series, which will be based on the sixth and seventh books in the series Joe Country and Slough House.
Slough House is an administrative purgatory for MI5 service rejects who have seriously failed a task but not badly enough to get sacked. Those consigned there are known as "slow horses", a play on the name of the place itself, Slough House, and an expression for people who are slow at thinking and action.
Those assigned there are expected to endure dull, routine tasks, along with occasional verbal abuse from their miserable boss, Jackson Lamb, who anticipates that they will leave out of boredom or frustration. Yet the slow horses somehow get involved in investigating cases that endanger Britain.
Slow Horses is based on the novel of the same name by Mick Herron , which is part of the author's Slough House series. It tells the story of a team of British intelligence agents who have all committed career-ending mistakes, and subsequently work in a dumping ground department of MI5 called Slough House. After a serious mistake, caused by a colleague but blamed on him, during a live training exercise at Stansted Airport , MI5 agent River Cartwright is demoted to dead-end work at Slough House, a tranche of MI5 reserved for the agency's screw-ups, headed by the alcoholic and impersonable Jackson Lamb.
Lamb assigns River to carry out surveillance on Robert Hobden, a journalist associated with far-right politicians Peter Judd and Roger Simmonds. River is then instructed to deliver the drive to the service's headquarters at Regent's Park , much to his surprise.
