Jackson Lamb (Gary Oldman), River Cartwright (Jack Lowden), and the rest of the Slough House reprobates are back for Slow Horses Season 4, and things are, unsurprisingly, not good. While a bombing in a bustling London shopping center consumes most of Britain’s intelligence community, River’s grandfather, David (Jonathan Pryce), has wandered into a very different sort of fight. His memory and cognitive skills are unraveling, triggering, among other problems, a rapid increase in his paranoia. One night, someone close to him drops in for a visit, and moments later, David guns down the visitor. But is everything what it seems?

Questions of what family members owe one another take center stage as David’s confused and deadly actions expose the previously largely unexplored complexity of the Cartwright family. As one member of Slough House runs to France to investigate a single errant clue, the rest of the team is left behind to protect David from Emma Flyte (Ruth Bradley), the new head of MI5’s “dogs”. While seemingly far less corrupt than her predecessors, she’s just as disinterested in tolerating the Horses’ nonsense or willing to trust their pleas for more time.

Coming at the Horses from the other side is a seemingly unstoppable black-ops mercenary (Tom Wozniczka) trying to clean up the loose ends of…something. David might have once been able to fill in the blanks, but with dementia steadily robbing him of his past and his present consumed with guilt and trauma, he can’t conjure any explanations. As he stalks the members of Slough House, Diana Taverner (Kristin Scott Thomas) tries to push the new First Chair, the hesitant and PR-focused Claude Whelan (James Callis), to bury anything and everything having to do with the bombing and its apparent perpetrator.

Of the new cast members, Hugo Weaving, as the season’s biggest villain, Frank Harkness, makes the biggest impression. He’s a braggadocious mastermind who pulls a move that felt ubiquitous in the action films of 2005-2015. It isn’t exactly an especially unusual character type. Still, Weaving invests a casual nastiness in Harkness that differentiates him enough to keep things interesting. The other new players get notably limited screen time, although, to be fair, almost everyone besides Lowden and Oldman feels like they’re doing more with less time.

Nonetheless, almost all of them prove plenty interesting. Bradley gives Flyte plenty of “the one honest person in espionage” energy, making her both an infuriating and respect-worthy foil for the fly by the seat of their pants antics of the Horses. Callis makes Whelan the worst sort of leader. His “ideals” are both inconvenient and immediately fall away the second he feels personally threatened. Tom Brooke’s new Horse, J.K. Coe, is possibly the season’s most intriguing newbie. Hooded, nearly silent, and unreadable, he proves a deeply unsettlingly and impressively loyal member of the team. Finally, the new secretary, Moira Tregorian (Joanna Scanlan), feels out of place in intelligence in general and Slough House especially. That is, until a flinty scene that leaves viewers wondering who’s the real Tregorian.

As mentioned briefly before, this season belongs mostly to Lowden and Oldman. And, really, more to Lowden than anyone. The actor’s grown into River every cycle, feeling increasingly comfortable in his skin. In Slow Horses Season 4, he’s plenty equal to shouldering the weight. There are two scenes where he shares a drink with another heavyweight actor. In both, he holds the frame with little to no dialogue. His body language is subtle but conveys everything those moments need.

While he’s the main attraction this time out, that doesn’t mean there aren’t some tasty moments for the rest. In particular, addicts Marcus (Kadiff Kirwan) and Shirley (Aimee-Ffion Edwards) maintain their old married couple chemistry until things get desperate, making the season finale all the more arresting. Pryce is excellent at capturing the terror of not being able to trust one’s own mind any longer. Finally, Rosalind Eleazar, one of the few still present Season 1 Horses Louisa Gay, gets her shots in early with standout moments in the first two episodes.

In my previous reviews, this critic has made significant hay out of how each season takes on a unique tone—while still feeling apiece with previous installments—that reflects the director’s unique sensibilities. I won’t belabor that point again, but Slow Horses Season 4 follows the pattern. I haven’t loved Adam Randall’s two previous efforts, the horror-action features Night Teeth and I See You. However, both feature strong stylistic choices and capture a certain adrenaline-heavy sense of momentum. Additionally, they feature familial and interpersonal dynamics that feel recognizable and in dangerous flux. Needless to say, Randall’s work here is the most satisfying deployment of his skills to date.

Slow Horses Season 4 gets out of the stables at AppleTV+ starting September 4.

Slow Horses Season 4 Trailer: