Half a dozen seasons deep, the lowest critical mark this Apple TV espionage series has ever recorded is 95%. That is the basement. Plenty of long-running dramas would treat that figure as a career-best peak, reached once and never again.
Spy dramas tend to run hot early and then sputter out somewhere around the third season. Once viewers learn the beats, surprising them gets harder and harder. This series figured out a way around that problem.
We’re talking about Slow Horses, built from Mick Herron’s Slough House novels, and its whole trick is taking the sleek super-spy fantasy and shoving it down a staircase. There are no flawless agents in bespoke suits rescuing the planet here.
What you get instead is a handful of washed-out MI5 officers dumped into the service’s administrative landfill, left to stew in the blunders that torpedoed their careers, all of it supervised by the ever-irritated Jackson Lamb, played by Gary Oldman.
The scores, season by season
Ever since the 2022 debut, reviewers and viewers have more or less agreed with each other about this one, a rarity in itself. Season 1 arrived with 95% from critics alongside 88% from audiences.
What followed is usually where series lose their footing. Instead, Season 2 hit a flawless 100% with critics and 90% with audiences, evidence that the concept had enough depth to support a second outing.
Season 3 eased back marginally to 98% among critics, paired with 89% from audiences. Season 4 bounced straight back up to 100%, once more with an 89% audience figure, and its Rotten Tomatoes consensus specifically pointed out that the show displayed “no signs of fatigue.”
Season 5 is where opinions diverged. Critics still put it at 96%, but the audience figure fell to 82% — the series low. Almost anywhere else on television, that counts as a triumph.
As things stand, Season 6 holds a spotless 100% critical score, with the audience tally still TBA. That makes three seasons at 100% to date. Across the whole run, the Tomatometer reads 98%.
Season 6 has a date
Apple TV renewed the show for a sixth season in October 2024, only a few days after the Season 4 finale went out. Hardly a surprise to anyone. It has been among the streamer’s more dependable prestige bets.
Season 6 arrives September 16, 2026, and advance reviews have been strong — which explains where that perfect score came from.
Why the floor never dropped
Right out of the gate, the series grasped that its characters count for as much as its plot machinery. The MI5 castoffs land because they are the inverse of the immaculate operatives the genre normally serves up.
Every member of the Slough House roster brings something to the table, though it would be dishonest to claim Oldman isn’t walking away with the whole show. Lamb initially scans as a profane, joyless boss with no regard whatsoever for his team. Beneath the abuse and the frankly disgusting personal habits, however, is a razor-sharp operative who understands precisely how to navigate a lethal world.
Its handling of tone matters as well. It’ll be comic in one beat and nerve-wracking in the next, and that pivot never feels manufactured. Rather than duplicate whatever landed previously, every season throws a brand new emergency at the Slough House crowd. Boredom never sets in.
Credit is due to the adaptation itself. Herron’s novels are page-turners of the unputdownable variety, and the series holds onto that while layering in character that a lesser version would have sanded away. Those source books took the CWA Gold Dagger Award, and the show treats that honor as earned.
Slough House is the dumping ground British intelligence uses for the personnel it would prefer to forget. Six seasons on, it’s the one address that has never slipped beneath 95%.