Apple TV+’s spy thriller series Slow Horses has managed to quietly put together one of the most impressive casts on television, featuring such stars as Gary Oldman, Olivia Cooke, and Kristin Scott Thomas. Based on Mick Herron’s series of spy novels, Slow Horses takes place at Slough House, an administrative purgatory for MI5 agents who have botched their jobs but haven’t been fired. Oldman leads the cast as Jackson Lamb, the curmudgeonly head of Slough House, alongside Jack Lowden as budding, up-and-coming agent River Cartwright.

Throughout its first three seasons, Slow Horses has been met with universal acclaim from critics, earning a perfect 100% Rotten Tomatoes score in its second season (with 95% for season 1 and 98% for season 3). The series has been praised for its fresh spin on the well-worn spy genre, its delightfully dark sense of humor, and its captivating cast of characters. Slow Horses has one of the best casts on TV right now – and season 4’s additions to the ensemble have made it even more impressive.

Slow Horses’ Season 4 Additions Make Its Already Impressive Cast Even Better

Hugo Weaving joins the ensemble

Each season of Slow Horses has introduced exciting new additions to the ensemble. Season 1 had an interesting role for House of the Dragon’s Olivia Cooke as competent secret agent Sid Baker. Season 2 brought in Rade Šerbedžija as former KGB agent Nikolai Katinsky and Harry Potter’s Adrian Rawlins as pub owner Duncan Tropper. Season 3 brought in Sope Dirisu to play Sean Donovan, the former head of security at the British embassy in Istanbul, and Alien: Covenant star Katherine Waterston to play MI5 insider Alison Dunn.

Slow Horses season 4 is continuing that proud tradition with some of the show’s most tantalizing castings to date. The great Hugo Weaving, best known as Agent Smith from The Matrix franchise and Elrond from The Lord of the Rings trilogy, has been cast to play a character named Frank Harkness. Humans’ Ruth Bradley has been cast as Emma Flyte, Battlestar Galactica’s James Callis has been cast as Claude Whelan, The Thick of It’s Joanna Scanlan has been cast as Moira Tregorian, and Preacher’s Tom Brooke has been cast as J.K. Coe.

Why Slow Horses Season 4 Is The Most Exciting Yet

And it’s not just because of the new cast members

Season 4 is the most exciting season of Slow Horses so far – and not just because of the new cast members. It’s based on the book Spook Street, which explores the idea of an aging spy who’s full of secrets and, as they get older and their mind starts to deteriorate, they start to forget that they’re supposed to keep those secrets to themselves. It’s a great jumping-off point for the series to continue its unique upending of familiar spy genre conventions. Slow Horses season 4 is set to premiere on Apple TV+ on September 4, 2024.