Slow Horses Season 6 Finally Gives Fans The Romance They've Been Waiting For

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This post contains spoilers for "Slow Horses" Season 6, Episode 5, "Sayonara."

Olivia Cooke's Sidonie Baker returned to "Slow Horses" early in Season 6 after having been presumed dead. The best thing to come out of Sid's return has been her banter with Jack Lowden's River Cartwright, with the pair picking up right where they left off prior to Sid being shot in Season 1. Now, in Episode 5, "Sayonara," Sid and River have finally expressed their feelings for one another in a surprisingly touching sequence that sees the latter pull a heroic move to save Sid from being shipped off to a certain death.

"Slow Horses" is about to run into a major problem previously faced by "Game of Thrones": It's running out of books to adapt. The Apple TV series is barreling through Mick Herron's novels at an impressive rate, and while that means fans are getting new episodes like clockwork, we're also approaching the end of Herron's official narrative for the Slough House sleuths. It doesn't help that Season 6 of the show adapts two novels for the first time in series history, combining books six and seven, "Joe Country" and "Slough House," into one narrative.

One major positive, however, is that fans have been able to see River and Sid express their feelings sooner than they might have otherwise. In Season 1, the two clearly had chemistry and seemed destined to share a slow-burn romance as the series went on. But after Sid was shot by Jed Moody (Steven Waddington), she disappeared and was officially pronounced dead. Now that she's back, she and River have had a chance to pick things back up, and in "Sayonara," we finally see them share a kiss in a nicely uplifting moment to counteract the chaos that surrounds them.

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If you thought "Slow Horses" was going to ease up following J.K. Coe's (Thomas Brooke) death, think again. In "Sayonara," Sidonie Baker is handed over to the Dogs (MI5's internal security team) to be sent off to Russia. It seems First Desk Diana Taverner (Kristin Scott Thomas) owes her Russian counterparts for having previously assassinated one of their agents and is offering up Sid as recompense. But as Taverner's assistant notes just prior to Sid's departure, her plane is actually bound for the Bulgarian capital of Sofia, which is neutral ground. That means Russia can effectively make Sid disappear, presumably by torturing and killing her.

Just before Sid is led to the aircraft, she and River Cartwright share some of their best banter, joking about whether the Russians will take her "somewhere romantic" to kill her. "What is a really romantic place to die?" asks River. "Pierced by the Eiffel Tower," Sid jokes. It's brilliantly funny in the classic understated "Slow Horses" way, yet also quietly agonizing as both characters recognize Sid's fate has essentially been sealed.

Soon after, Sid and River stand on the tarmac and finally acknowledge their feelings, with Sid saying she would leave a light on for River when he comes home at the end of the day, just like his late grandfather used to do. It's taken her impending death for her to finally say something, but at least it's out. As she's led away, River takes matters into his own hands, stealing a truck, picking up Sid, and driving her away from the air base before dropping her off and allowing her to escape while he distracts the Dogs. Before they part ways, they share a kiss six seasons in the making.

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Sid Baker and River Cartwright's romance has been a long time coming. After Sid was shot and presumed dead in Season 1, the show seemed to set up River and Louisa Guy (Rosalind Eleazar) as potentially having feelings for one another, only to quickly pull that rug out when we learned that Louisa was not into it after all. But as great as Jack Lowden and Eleazar's chemistry was, there's no doubt his and Olivia Cooke's is one of the best things about "Slow Horses." 

With River having suffered the loss of his grandfather after a lengthy struggle with Alzheimer's, and having to deal with the return of his murderous father Frank Harkness (Hugo Weaving) at the start of "Slow Horses" Season 6, it's been rough going for the guy. Fans will no doubt be thrilled to see his long-awaited romance with Sid finally blossom.

Cooke spoke to Town and Country about Sid and River's relationship, pointing to how the pair had "a heavy dose of limerence" between them in Season 1, in which Sid was assigned to tail River. "It was sort of forbidden," she said. "This was the person that she was meant to be tracking and tailing and reporting back to Diana Taverner on. But they do have this undeniable chemistry, and in her absence, this fantasy of River had only just gotten bigger." 

That's partly what makes River and Sid's kiss feel like such a momentous development. Their relationship was tragically cut short back in Season 1, and thanks to Cooke and Lowden's performances, you can feel all the pent-up longing expressed in these brief scenes at the end of "Sayonara." We knew the pair had chemistry, but to see them connecting emotionally during such a high-intensity moment makes this one of the series' best episodes.