Why did Jackson Lamb murder Charles Partner in Slow Horses? Details explored in depth

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Slow Horses (Image via AppleTV+)
Slow Horses (Image via AppleTV+)

Apple TV+’s Slow Horses is a British spy drama built around the forgotten end of MI5, agents who’ve made mistakes serious enough to get kicked out of frontline service, but not bad enough to be fired outright. These agents are dumped at Slough House, a run-down office in London, under the control of Jackson Lamb, a bitter, foul-mouthed, chain-smoking former field agent who treats them like they’re already dead weight.

Slow Horses is based on Mick Herron’s Slough House novels and leans into the idea that the real work of espionage isn’t sleek missions or gadgets; it’s paperwork, political cover-ups, and cleaning up after your own agency’s mistakes.

Each season follows these “slow horses” getting caught in something bigger than they were ever meant to handle, from hostage situations and sleeper agents to Russian moles and decades-old secrets. At the center is Lamb, who might act like a lazy drunk but has done more for national security than half the higher-ups behind desks.

One of the deepest scars from his past involves the murder of a former MI5 Second Desk, Charles Partner, a man Lamb once trusted, then had to kill. That event quietly shaped everything that followed.


The real reason Jackson Lamb murdered Charles Partner in Slow Horses, explained

Slow Horses (Image via AppleTV+)
Slow Horses (Image via AppleTV+)

Jackson Lamb didn’t kill Charles Partner out of anger, revenge, or personal hatred. He killed him because MI5 needed him to. Partner wasn’t just a high-ranking official at the top of the service; he was the Second Desk, someone deeply trusted and close to the agency’s inner circle. But behind all that polish and credibility, he had been feeding secrets to the Russians for years.

Not just low-level stuff, but intelligence that risked operations, exposed assets, and compromised allies. This kind of betrayal could’ve wrecked the agency from the inside if it became public.

Lamb, during his Cold War years, was stationed in Berlin. That’s where he started piecing things together. He wasn’t some paperwork guy stuck behind a desk. He was in the field, dealing with informants, making dead drops, and losing agents to Russian counter-intelligence.

When Partner’s name started popping up in places it shouldn’t have, Lamb knew something was off. And once the evidence lined up, it became impossible to ignore. Partner wasn’t just making mistakes—he was actively working for the enemy.

Instead of blowing the whistle and triggering a massive scandal, MI5 wanted the problem buried. They couldn’t afford a public trial and couldn’t risk foreign governments seeing how deeply their own ranks had been infiltrated. So, someone had to take care of it quietly.

That someone was Jackson Lamb. He had the clearance, the access, and the reputation for getting dirty jobs done. So, he went to Partner’s flat, killed him in his bathtub, and made it look like suicide.

Slow Horses (Image via AppleTV+)
Slow Horses (Image via AppleTV+)

This wasn’t a quick decision or a heated moment. It was a planned execution, carried out as damage control. And Lamb didn’t do it with glory in mind. He didn’t get promoted afterward. He didn’t even get thanked. What he got was a slow demotion into obscurity.

Slough House became his punishment, a place to keep him out of the way, surrounded by washouts and red-tape screw-ups. But Lamb knew what he had done had saved the agency from an internal collapse. He took the weight so the institution could survive.

Slow Horses teases this backstory across the first two seasons, mostly through offhand remarks and bits of quiet tension between Lamb and Diana Taverner, who once saw Partner as a mentor.

In the books, the situation is laid out with more detail, specifically in Dead Lions, where past and present collide around an old Cold War relic found dead on a bus. That’s when the Partner story starts to take shape, showing how much was sacrificed to protect the Service’s image.

Lamb doesn’t justify what he did. He doesn’t even bring it up unless cornered. But his silence says everything. He knows it was ugly. He also knows it was necessary.


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Edited by Debanjana