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Mick Herron's 2010 spy novel Slow Horses is being made into a TV series, reports Empire online. It was already announced that Gary Oldman (Darkest Hour) would take on the lead role, and now Kristin Scott Thomas (The Party) has joined the cast.

The story revolves around an unorthodox MI5 leader by the name of Jackson Lamb (Oldman). He oversees a group of agents who are just as edgy as he is.

They all find themselves on this team as they each have "screwed up royally" and will do anything to redeem themselves, according to the book description.

Thomas is set to portray Diana Taverner, a powerful, but conflicted, agent.

In addition to Oldman and Thomas, we can also look for Jonathan Pryce (The Wife) as a retired agent and Jack Lowden (Small Axe) as River Cartwright, the latest agent to be exiled (also the grandson of Pryce's character).

River is assigned the monotonous job of transcribing cell phone conversations. When he overhears a kidnapping scheme, he sees it as his way to get out of this dead-end job.

Slow Horses is the first installment of Herron's Slough House series, which is made up of eight books total.

If the first season goes off well, there is plenty more material to pull from.

While it's in the early stages, the series is being written by Will Smith (Avenue 5) for Apple.

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