Season 4 of Slow Horses has arrived on Apple TV+, and though we only have access to one episode so far – the streamer has opted for a weekly release schedule – it's quite an explosive one.

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Yes, that's right, another beloved character met a dramatic end in the opener of the spy drama, based on Mick Herron's Spook Street.

That, viewers will be used to – the series doesn't shy away from killing off main characters – but, this time around, its expanding its core cast to include even more big names.

Gary Oldman is back as Jackson Lamb. Jack Lowden and Kristin Scott Thomas will be joining him, as will some brand new faces, including Hugo Weaving as Frank Harkness, and Tom Brooke, playing the mysterious JK Coe.

Not only that, but cast and crew have already discussed new characters joining in season 5, which has already been confirmed.
Saskia Reeves, who plays Lamb's secretary Catherine Standish, recently said: "We also have the opportunity of bringing in new characters, and therefore new actors and different actors. There's lot to look forward to."
Roddy Ho actor Christopher Chung also addressed future characters, adding: "They all just change the dynamic slightly, and it throws up more questions for each of our characters every time we get to interact with a new cast member.

"And I think that's the thing that's quite exciting about looking forward to whatever in the future, is that you can continue to ask these questions because they're always getting thrown by whoever is coming in."

Read on for everything you need to know about the cast of Slow Horses season 4 on Apple TV+.

Who’s in the cast of Slow Horses season 4?

Below is the main line-up for Slow Horses season 4, which is now releasing episodes on Apple TV+. Read on to find out more about the cast and characters.

  • Jack Lowden as River Cartwright
  • Gary Oldman as Jackson Lamb
  • Saskia Reeves as Catherine Standish
  • Kristin Scott Thomas as Diana Taverner
  • Rosalind Eleazar as Louisa Guy
  • Christopher Chung as Roddy Ho
  • Aimee-Ffion Edwards as Shirley Dander
  • Kadiff Kirwan as Marcus Longridge
  • Jonathan Pryce as David Cartwright
  • Hugo Weaving as Frank Harkness
  • Joanna Scanlan as Moira Tregorian
  • Ruth Bradley as Emma Flyte
  • James Callis as Claude Whelan
  • Tom Brooke as JK Coe

Jack Lowden plays River Cartwright

Jack Lowden as River Cartwright in Slow Horses season 4
Jack Lowden as River Cartwright in Slow Horses season 4 Apple

Who is River Cartwright? River is an agent at Slough House who was sent there for botching a mission.

Where have I seen Jack Lowden before? Lowden had a leading role in the BBC's War and Peace, and has since appeared in Small Axe, Mary Queen of Scots and Stephen Merchant's Fighting with My Family. He also had a pivotal role in Christopher Nolan's 2017 epic Dunkirk, and recently appeared in The Gold on BBC One.

Gary Oldman plays Jackson Lamb

Gary Oldman as Jackson Lamb in Slow Horses. He is taking a phone call
Gary Oldman as Jackson Lamb in Slow Horses. Apple

Who is Jackson Lamb? Jackson is the leader of Slough House. He's a "brilliant but irascible" leader, who has a terse, barbed relationship with River and has a dark past.

Where have I seen Gary Oldman before? Oldman has had a long and storied career on the big screen, appearing in blockbusters such as the Harry Potter series and The Dark Knight trilogy, alongside awards darlings such as Mank and Tinker Tailor Soldier Spy. He's been Oscar nominated three times, winning Best Performance by an Actor a Leading Role in 2017 for playing Winston Churchill in Darkest Hour.

Saskia Reeves plays Catherine Standish

Saskia Reeves in Slow Horses, stood in a doorway
Saskia Reeves in Slow Horses Apple TV+

Who is Catherine Standish? Catherine is Lamb's former personal assistant, who quit at the end of season 3. She knows the ins and outs of Slough House.

Where have I seen Saskia Reeves before? Reeves is known for appearing in series such as Luther, Death in Paradise, Collateral, Silent Witness and Wolf Hall, as well as in series such as Nymphomaniac: Vol 1 and Shadows.

Kristin Scott Thomas plays Diana Taverner

Kristin Scott Thomas in Slow Horses
Kristin Scott Thomas in Slow Horses Apple TV+

Who is Diana Taverner? Diana is the second desk at MI5, who has worked with Lamb and his agents in the past but is very willing to let them take the fall for her mistakes.

Where have I seen Kristin Scott Thomas before? Scott Thomas reunites with Oldman in Slow Horses, having played Churchill's wife Clementine in Darkest Hour. She's perhaps best known for her BAFTA role in Four Weddings and a Funeral, but has also won plaudits for roles in The English Patient, Nowhere Boy and Gosford Park, amongst others. She was made a Dame in 2015.

Rosalind Eleazar plays Louisa Guy

Rosalind Eleazar in Slow Horses, crouched down
Rosalind Eleazar in Slow Horses Apple TV+

Who is Louisa Guy? Louisa is a member of Slough House and one of the most affective agents in the group.

Where have I seen Rosalind Eleazar before? Eleazar has appeared in series including Breeders, Master of None, Deep Water and Death in Paradise, as well as the films Uncle Vanya and The Personal History of David Copperfield. She will soon be seen in Harlan Coben's Missing You.

Christopher Chung plays Roddy Ho

Christopher Chung as Roddy Ho in Slow Horses, sat in a fast food restaurant talking on the phone
Christopher Chung as Roddy Ho in Slow Horses Apple TV+

Who is Roddy Ho? Roddy is the team's tech guy, who is abrasive and uncaring towards the rest of the group and likes to stay out of the field.

Where have I seen Christopher Chung before? Chung has previously appeared in Waterloo Road and Neighbours amongst other roles.

Aimee-Ffion Edwards plays Shirley Dander

Aimee-Ffion Edwards in Slow Horses, with wet hair and wearing a jumper
Aimee-Ffion Edwards in Slow Horses Apple TV+

Who is Shirley Dander? Shirley is a member of the team at Slough House who has noted anger issues and problems with drug abuse.

Where have I seen Aimee-Ffion Edwards before? Edwards is perhaps best known for her role as Esme in Peaky Blinders, while she has also starred in Keeping Faith, Inside No 9, Death in Paradise, Detectorists, Luther and Dreamland.

Kadiff Kirwan plays Marcus Longridge

Kadiff Kirwan as Marcus Longridge in Slow Horses
Kadiff Kirwan as Marcus Longridge in Slow Horses Apple TV+

Who is Marcus Longridge? Marcus is a member of Slough House who is trying to get his gambling addiction under control for the sake of his family.

Where have I seen Kadiff Kirwan before? Kirwan has had roles in series including Black Mirror, Chewing Gum, Strike, Fleabag, Timewasters, The Stranger, This Way Up, This is Going to Hurt and Everyone Else Burns, as well as films such as My Policeman.

Jonathan Pryce plays David Cartwright

Jonathan Pryce as David Cartwright in Slow Horses
Jonathan Pryce as David Cartwright in Slow Horses season 4 Apple

Who is David Cartwright? David is the River's grandfather and is himself a retired MI5 agent. He and Jackson have a dark past together, and since the end of season 3 he is showing signs of dementia.

Where have I seen Jonathan Pryce before? Pryce played Prince Philip in the fifth and sixth seasons of Netflix's The Crown. He has already unsettled us as the High Sparrow in Game of Thrones and enthralled us as Pope Francis in The Two Popes, while also appearing in the Pirates of the Caribbean series, in James Bond adventure Tomorrow Never Dies and recently in 3 Body Problem. He was knighted in 2021.

Hugo Weaving plays Frank Harkness

Hugo Weaving as Frank Harkness in Slow Horses season 4
Hugo Weaving as Frank Harkness in Slow Horses season 4 Apple

Who is Frank Harkness? Frank is a mercenary, and a villainous character who is introduced in season 4. Weaving has said of his character: "He's ruthless, but he's not without charm. And I'd say in this season, we see quite a lot of urbanity. He's quite an urbane character, but you feel that he's got a lethality, a physicality and a lethality to him as well."

Where have I seen Hugo Weaving before? Weaving is best-known for his roles as Elrond in Lord of the Rings and as Mr Smith in The Matrix trilogy. He has also appeared in the Transformers series, played Red Skull in Captain America: The First Avenger and had memorable roles in V for Vendetta, The Adventures of Priscilla, Queen of the Desert and Patrick Melrose.

Joanna Scanlan plays Moira Tregorian

Joanna Scanlan as Moira Tregorian in Slow Horses season 4
Joanna Scanlan as Moira Tregorian in Slow Horses season four. Apple

Who is Moira Tregorian? Moira is Catherine Standish's replacement at Slough House, who is desperate to get back to the Park.

Where have I seen Joanna Scanlan before? Scanlan is perhaps best known for her role as Terri in The Thick of It, while she has also appeared in Big School, The Bad Education Movie, Bridget Jones's Baby, No Offence, Dracula, Gentleman Jack, The Larkins, Wicked Little Letters and Boat Story, amongst other series and films.

Ruth Bradley plays Emma Flyte

Ruth Bradley as Emma Flyte in Slow Horses standing in a station looking concerned
Ruth Bradley as Emma Flyte in Slow Horses. Apple

Who is Emma Flyte? Emma is the new leader of the Dogs, taking over from Nick Duffy who was left in a coma following season 3.

Where have I seen Ruth Bradley before? Bradley has previously had roles in series such as Primeval, The Fall, The Split, Humans, The Gold, Guilt and Ted Lasso, as well as films such as The Wonder.

James Callis plays Claude Whelan

Kristin Scott Thomas as Diana Taverner and James Callis as Claude Whelan in Slow Horses season 4
Kristin Scott Thomas as Diana Taverner and James Callis as Claude Whelan in Slow Horses season 4 Apple TV+

Who is Claude Whelan? Claude is the new first desk at MI5, having replaced Ingrid Tearney over Diana, who expected to get the job. He is well-meaning and wants to clean up the organisation, but is seriously under qualified.

Where have I seen James Callis before? Callis is best-known for his roles in Battlestar Galactica and Bridget Jones's Diary, while he has also appeared in Merlin, A Town Called Eureka, The Musketeers, Castlevania and Star Trek: Picard.

Tom Brooke plays JK Coe

Tom Brooke as JK Coe in Slow Horses, with his hood up
Tom Brooke as JK Coe in Slow Horses Apple TV+

Who is JK Coe? Jason Kevin Coe, who goes by JK, is a new mysterious addition to Slough House. He stays mostly silent and just wants to be left alone. Brooke has revealed that the character has PTSD, which he keeps in check by pretending to play the piano.

Where have I seen Tom Brooke before? Brooke has had roles in series such as Game of Thrones, Sherlock, Bodyguard, Preacher and The Crown, as well as in films including The Death of Stalin and Empire of Light.

Slow Horses season 4 will stream on Apple TV+ from Wednesday 4th September – sign up to Apple TV+ now.

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