When does Slow Horses return?

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. Those assigned there are expected to endure dull, routine tasks, along with occasional verbal abuse from their miserable boss.
Slough House is an administrative purgatory for MI5 service rejects who have bungled their job but have not been sacked. Those consigned there are known as "slow horses" - a pun on "Slough House" They are expected to endure dull, paper-pushing tasks, along with occasional mental abuse from their miserable boss, Jackson Lamb.