‘Slow Horses’ author Mick Herron reveals the secret origins of Slough House

In the middle of a conversation about “Clown Town,” the new Slow Horses novel, author Mick Herron reveals a bit of previously untold lore about the origins of Slough House.

Referring to a team of older spies who appear in the just-published book, Herron says, “Their careers never really went in the direction that they should have, very similar to the way the Slow Horses have been treated,” the latter referring to his recurring cast of misbegotten MI5 agents. “But of course, this is way back when Slough House itself didn’t exist at the time they were on active duty, so there was never any chance that they would have been sent there.”

Balancing gripping espionage, office tensions and Herron’s deeply funny prose, the Slow Horses books focus on M15’s fictional Slough House unit: the career