Exclusive: Slow Horses boss breaks silence on ‘odd’ River and Louisa romance and look ahead to ‘dark’ season 6

Slow Horses season five will return to Apple TV+ this September – and we can expect “thrills and chills, surprises, double backs, backstabbing, the decay of society and the usual things,” according to showrunner Douglas Urbanski.

Speaking to HELLO! at the Television Academy’s Televerse Festival in Los Angeles Douglas admitted it’s hard to discuss season five – which premieres on September 24, 2025 – because the crew are already in post-production on season six.

“I know too much!” he said, adding: ‘If you think that each season has its own personality, and it does, each season should feel a little bit different than every other season.

“Season five is the ‘silly season’. Silly, because Roddy Ho (Christopher Chung) is the main character, and he’s the more outlandish of them all.”

However, he added: “Going into season six, that will be the ‘dark season,’ as you’ll see, big things happen.”

Season four uncovered personal secrets for River Cartwright (Jack Lowden), and Douglas shared that in season five viewers will see Grandpa Cartwright (Sir Jonathan Pryce) who is now living in a care home but who “has still got connectivity to things that happen”.

“Season four was all about going back to the River thing,” he said.

“And of course, Jackson Lamb (Sir Gary Oldman) has a connectivity with all these characters as well – the bad guys always want to kill either Lamb or Grandpa Cartwright, and they are still going after them.”

Sir Gary told HELLO! season five will also see Lamb get more screen time with Roddy, an opportunity that he relished because “I love and only ever interact with [Chris] in passing and in insults [on screen]”.

“[The Slow Horses] often go off as a team, as a gang, and [Jackson is] at the desk, feet up, giving orders and then investigating as a solo, so it was nice to spend many weeks coming in and working with Chris.”

In season four there was heartache for the Horses when Marcus was gunned down, an arc that will heavily impact the team moving forward especially for Shirley.

“Shirley is a person who has anger management issues, a drug issue, and she’s missing her pal,” said Douglas. “But Marcus was a special character, and every time a slow horse dies, it affects them all.”

Across the first five seasons, viewers have found a sweet chemistry in the connection between River and Louisa Guy (Rosalind Eleazar).

But Douglas has, however, warned fans from getting too invested in the potential for a love story.

“It’s an odd thing,” said Douglas.

“I wonder how many people have actually had workplace chemistry that didn’t amount to anything, or a workplace flirtation where both people knew that’s exactly what it was and that’s where it will remain. I think that there’s some of that going on.”

Slow Horses season five will return to Apple TV+ this September – and we can expect “thrills and chills, surprises, double backs, backstabbing, the decay of society and the usual things,” according to showrunner Douglas Urbanski.

Speaking to HELLO! at the Television Academy’s Televerse Festival in Los Angeles Douglas admitted it’s hard to discuss season five – which premieres on September 24, 2025 – because the crew are already in post-production on season six.

“I know too much!” he said, adding: ‘If you think that each season has its own personality, and it does, each season should feel a little bit different than every other season.

“Season five is the ‘silly season’. Silly, because Roddy Ho (Christopher Chung) is the main character, and he’s the more outlandish of them all.”

However, he added: “Going into season six, that will be the ‘dark season,’ as you’ll see, big things happen.”

Season four uncovered personal secrets for River Cartwright (Jack Lowden), and Douglas shared that in season five viewers will see Grandpa Cartwright (Sir Jonathan Pryce) who is now living in a care home but who “has still got connectivity to things that happen”.

“Season four was all about going back to the River thing,” he said.

“And of course, Jackson Lamb (Sir Gary Oldman) has a connectivity with all these characters as well – the bad guys always want to kill either Lamb or Grandpa Cartwright, and they are still going after them.”

Sir Gary told HELLO! season five will also see Lamb get more screen time with Roddy, an opportunity that he relished because “I love and only ever interact with [Chris] in passing and in insults [on screen]”.

“[The Slow Horses] often go off as a team, as a gang, and [Jackson is] at the desk, feet up, giving orders and then investigating as a solo, so it was nice to spend many weeks coming in and working with Chris.”

In season four there was heartache for the Horses when Marcus was gunned down, an arc that will heavily impact the team moving forward especially for Shirley.

“Shirley is a person who has anger management issues, a drug issue, and she’s missing her pal,” said Douglas. “But Marcus was a special character, and every time a slow horse dies, it affects them all.”

Across the first five seasons, viewers have found a sweet chemistry in the connection between River and Louisa Guy (Rosalind Eleazar).

But Douglas has, however, warned fans from getting too invested in the potential for a love story.

“It’s an odd thing,” said Douglas.

“I wonder how many people have actually had workplace chemistry that didn’t amount to anything, or a workplace flirtation where both people knew that’s exactly what it was and that’s where it will remain. I think that there’s some of that going on.”