Why Slow Horses is so good – Every season ranked

The show that should not work

Write the pitch down and it reads like a rejection letter. A spy series with no gadgets. No exotic locations to speak of. A lead character who is overweight, filthy, permanently drunk and openly contemptuous of everyone around him. The setting is a damp office above a Chinese takeaway in a part of London nobody visits on purpose. The heroes are, explicitly and without irony, bad at their jobs.

And yet Slow Horses is the best spy show on television, and it is not especially close.

The reason is structural. Espionage fiction has always run on competence. Bond is the best; Jack Ryan is the smartest person in the situation room; Clancy’s whole architecture rests on the assumption that when the machine is properly staffed, the machine works. That is a legitimate and enormously enjoyable fantasy, and there is a shelf of paperbacks in most of our houses to prove it — the Frederick Forsyth hub covers its purest form, where even the assassin is simply very good at his job, and the Jason Bourne hub covers the version where that competence turns on the people who installed it.

Mick Herron’s premise is the opposite, and it is far better fuel for a thriller. Slough House exists because MI5 cannot easily fire people. So the ones who lost a disk on a train, or drank, or gambled, or froze at the wrong moment get sent to an annexe where the work is deliberately meaningless and the hope is that they will resign out of sheer tedium. When something real happens, these are the people who catch it — not because they are chosen, but because everyone competent is busy protecting their own position.

Four reasons it beats the glossy competition

1. Failure makes the stakes real

In a competence thriller, tension comes from scale: a bomb, a city, a country. In Slow Horses, tension comes from the credible possibility that these specific people will mess it up, because you have watched them mess things up before. When a Slow Horse dies, and they do, it does not feel like a plot beat. It feels like the natural consequence of sending underqualified people into something serious with no support.

That is also why the show can be genuinely funny without deflating itself. The comedy and the danger come from the same source.

2. Jackson Lamb is a great character, not a great gimmick

Gary Oldman never once asks you to like Jackson Lamb. He is vile to the people who deserve it least, particularly Catherine Standish, the recovering alcoholic who keeps his office upright. The show resists every opportunity to give him a redemptive speech.

What it does instead is show you, repeatedly and without comment, that Lamb will not let one of his people be written off. He fights over a dead officer’s family payment. He refuses a convenient verdict on a death. He does the paperwork nobody asked him to do. The character works because the decency is entirely in the actions and never in the dialogue, which is a harder trick than it sounds and the reason the performance has collected the nominations it has.

3. The dialogue survives the adaptation

Herron writes the funniest, cruellest dialogue in the genre, and Will Smith’s scripts for the first five seasons keep it largely intact. A single scene will typically hand you a joke, a piece of plot and a character revelation inside forty seconds. Very little television respects your attention that much, and it is the main reason a 45-minute episode of this feels denser than an hour of almost anything else.

4. Six episodes, and then it stops

Every season is six episodes of roughly 45 minutes. That is about four and a half hours: one weekend, or a fortnight of school nights. There is no eight-episode contractual padding, no mid-season detour, no episode that exists to fill a slot. The story ends when it is finished.

If you have a limited number of evenings and a 6am alarm, this is not a minor virtue. It is arguably the single most persuasive thing about the show.

Every season ranked

Full reviews for each are in the cards above. The short version:

1. Season 1 (5/5) — the only perfect one. Six episodes, zero filler, a proper kidnapping thriller and the arrival of Lamb. Start here, always.
2. Season 3, Real Tigers (4.5/5) — the most propulsive. They take Catherine Standish and the show turns feral, ending with an assault on Slough House itself. The one you will describe to people.
3. Season 4, Spook Street (4.5/5) — the best acted and the bleakest. Jonathan Pryce as a spymaster losing his memory, Hugo Weaving as the series’ best villain, and a loss the show refuses to soften.
4. Season 2, Dead Lions (4.5/5) — the most melancholy. Cold War sleepers waking up in the home counties, and the death that taught the audience nobody here is safe.
5. Season 5, London Rules (4/5) — the most shocking opening and the thinnest conspiracy. Still gives Roddy Ho the best material of his life.

The gap between first and fifth is smaller than the numbers suggest. There is no bad season of this show, only one that lets you see the machinery.

If you loved the Clancy novels

This is the specific recommendation. If your route into the genre was Tom Clancy paperbacks, and you have since found the prestige adaptations slick, expensive and somehow weightless, Slow Horses is the correction — but you should know what you are trading.

You lose the geopolitics, the hardware, the sense of a functioning apparatus. You gain characters who can actually be hurt, an institution that behaves like every institution you have ever worked inside, and prose-quality dialogue.

If you want to see where the competence engine finally runs out of road, The Teeth of the Tiger is Clancy’s last solo Ryanverse novel and a handover book in every sense — a sharp premise carried by a next generation the series never quite convinces you has earned it. Read it and then watch a season of Slough House, and the contrast makes the argument better than any paragraph here can. Debt of Honor is the better example of the machine running at full strength, if you want to see the version that still works before it starts to wobble.

If Clancy’s hardware is more than you want, Vince Flynn strips the competence engine down to nothing but the capable person — Transfer of Power is the cleanest entry point, and The Third Option is the one where that competence briefly runs into a problem it cannot just shoot its way through.

The closest neighbour on our shelf is Andor, which sounds absurd until you notice both are grounded thrillers about how bureaucracies fail the people inside them, and both are far more interested in logistics and cowardice than in heroics. If you want the tuxedo version instead, our Casino Royale review covers the last time Bond was allowed to bleed properly.

Season 6: Now airing

Three things stand out. The first is that Season 6 adapts two novels rather than one, which is a change of gear for a show whose great discipline has been one book, six episodes, no padding. Combining Joe Country with the following book suggests a season built to move rather than to simmer, and the official line about the team being on the run supports that.

The second is the writing change. Will Smith adapted all five previous seasons and won a Primetime Emmy for it. Gaby Chiappe takes over here, with Adam Randall returning to direct after Season 4. Randall handled the show’s most emotionally punishing year, which is not a neutral signal.

The third is Olivia Cooke. Sid Baker was shot in Season 1 and reported dead, and her absence has hung over River Cartwright for four seasons. Apple has confirmed Cooke returns as Sid in Season 6, which is the sort of resurrection this show has never gone in for, and the reason it is the most interesting thing on the slate. Hugo Weaving is also back as Frank Harkness, and Lenny Rush joins the cast.

How to use this page

The cards above link to our full review of each season, with ratings, age guidance and spoiler-light plot detail. If you are starting from nothing, read the Season 1 review and then stop reading and go and watch it. If you are caught up and waiting, the Season 5 review covers where the team is left standing, which is the state Season 6 inherits.

The novels are the other route in. Each season maps to one book, in order — the full mapping lives on the Slow Horses hub — so reading one ahead of the show is entirely possible and very enjoyable. The audiobooks are particularly good if your reading time is really commuting time — Audible’s 30-day trial is enough to test whether the Slough House voice survives a school run, though check what is in the catalogue on the day rather than assuming.

The Dadnology verdict

Slow Horses is the rare long-running show that has never wasted an episode of your time. It is funny in a way that makes the danger worse rather than better, it is written with a density almost nothing else on streaming attempts, and it contains a lead performance that will be taught to actors in twenty years.

Five seasons in, it has lost a little of its capacity to surprise and none of its craft. Season 6 arrives on 16 September 2026 with two novels to burn through, a returning director, a new writer and a character back from the dead. That is either a show finding a second gear or a show reaching for one. Either way, we will be watching it weekly, one episode at a time, like it is 2006.

Why is Slow Horses so good?

Because it inverts the genre’s founding assumption. Almost every spy story runs on competence: the hero is the smartest person in the room. Slow Horses runs on failure. Its characters are the ones MI5 could not be bothered to sack, which makes every small victory cost something and every institutional betrayal land properly.

What is the best season of Slow Horses?

Season 1 is the only perfect one for us, at 5 out of 5. Season 3 is the most exciting and Season 4 the best acted, both at 4.5. Season 2 matches them and is the most melancholy. Season 5 is the weakest at 4 out of 5, which still puts it above most of its competition.

Do I need to read the books before watching Slow Horses?

No. Each season adapts one novel closely enough to stand alone, and the show is designed for viewers who have never heard of Mick Herron. The books are an excellent follow-up, and reading one season ahead is the most enjoyable way to do it.

Is Slow Horses better than Jack Ryan?

For our money, comfortably. Jack Ryan is a competence fantasy with a large budget and a globe-trotting brief. Slow Horses is a character study with better dialogue, real consequences and a lead performance that is genuinely one of the great ones. They are aiming at different things, and Slow Horses hits its target far more often.

When does Slow Horses Season 6 come out?

Season 6 premiered on Apple TV on Wednesday 16 September 2026 and is airing now, with new episodes released weekly through to 21 October 2026. It adapts Joe Country and Slough House, the sixth and seventh novels in Mick Herron’s series.

Where should I start with Slow Horses?

Season 1, episode 1. There is no shortcut and no better entry point. The series is a single linear story with a fixed cast, and the emotional payoffs in later seasons depend entirely on time served with these people.