Slow Horses Season 3 Ending, Explained: What Is In The Footprint File?

The MI5 Agents at Slough House, under seasoned and cynical Jackson Lamb’s leadership, face an enormous inside threat in the third season of Apple TV+’s spy thriller show, ‘Slow Horses.’ The Service’s designated dumping ground, Slough House, populated with agents like River Cartwright, Louisa Guy, Roddy Ho, and newest addition Shirley and Marcus, is used to having their backs against the wall. However, when one of their own, an administrative worker, Catherine Standish, gets taken hostage in a power grab plot, the horses must do their best to rescue her. In the process, new conspiracies are unearthed, with one ex-agent, Sean Donovan, and his partner’s mysterious death at the center.

This season of the show revolves around a well-kept secret that builds upon itself and proves to be much more volatile for Lamb, his agents as well as the entire MI5 Agency. Therefore, fans must be curious to learn more about the elusive Footprint files, its fate, and how it takes MI5 by storm, forever leaving it changed in its wake. SPOILERS AHEAD!

Slow Horses Season 3 Recap

After the events of Season 2, Diana Taverner reckons with the consequences of her actions that strip away some of her power at the MI5 Headquarters, the Park. In turn, she’s assigned authority over a filing facility, currently stocked with negligible files from the Slough House of all places. For the same reason, River Cartwright, the department’s most eager-for-action agent, remains perpetually annoyed at the filing assignments Standish keeps piling on him. Nevertheless, his contention against uneventfulness becomes ill-timed when Standish soon goes missing.

As a result, Lamb’s instinct tips him off, compelling him to look for the woman with his agents. Soon, confirmation arrives about Standish’s abduction when her kidnapper, Sean Donovan, an ex-MI5 Agent with an unpleasant past with the Agency, sends River a ransom text. Thus, with a short-time crutch on his head, River receives instructions to break into the Park and steal the PM Vetting files in exchange for his co-worker’s life.

Operating under immense stress and fear for Standish’s life, River manages to get a foot inside the Park’s highly classified level despite lack of clearance by tricking an old rival, Nick Duffy. Meanwhile, Louisa finds a clue, connecting Standish’s kidnapping to a man named Sean Donovan, whose position as a special operative rouses Lamb’s suspicions. With the help of an old acquaintance, the man figures out that a private security company is behind the kidnapping and is compelling River to do their bidding.

The same leads Lamb to realize Donovan is likely part of a Tiger Team, set up to test the security measures at The Park by people in higher authority. Therefore, even though River manages to make it into the HQ’s archives after some trouble, he leaves without the file on Lamb’s orders. Nevertheless, the damage remains done.

Consequently, Ingrid Tearney, MI5’s First Desk Director-General, finds herself in hot water with Home Secretary Judd, who had planted the Tiger Team through Chieftan’s private security services. However, when the Chieftans send in their agent to retrieve Standish, Donovan’s team kidnaps him, signaling they have gone rogue. Simultaneously, Lamb figures out that the Tiger Team is actually after MI5’s archives of conspiracies, the Gray Books, which are located in Diana’s filing facility.

Still, Lamb and the others believe the rogue team won’t harm their agents just yet. However, Spider, an ex-service agent turned Chieftan employee, throws a wrench in the theory when his meeting with Donovan leads to an unpleasant altercation wherein the former man dies. As such, Ingrid agrees to wrap up the mess created by Judd’s plan to save MI5’s reputation. Yet, Lamb declines when she tries to loop him into working for her.

Nonetheless, Ingrid needs a Slough agent for her plan so that she can use the department as a scapegoat, leading her to contact River. As such, she forms a plan to allow Standish’s kidnappers to look into the Gray Books, deeming them relatively inconsequential, and asks River to escort them to the facility. However, once River and Donovan enter the facility, each with their respective backups, Louisa and Ben, Ingrid discovers about Donovan and his past connection to the Footprint file through Alison. Consequently, she deploys Duffy and a cavalry of Chieftan agents to kill everyone inside the file facility.

Slow Horses Season 3 Ending: The Footprint File

The Footprint file remains the biggest mystery this season, its introduction jumpstarting the narrative. Alison Dunn and Sean Donovan, two MI5 Agents in a secret relationship with one another, have assignments in Istanbul. However, their relationship comes crashing down once Alison realizes Donovan has been tasked to investigate her alleged betrayal of MI5. The Service suspects Alison of possessing and scheming to leak the Footprint File. As it would turn out, they weren’t wrong.

Nevertheless, Alison tries to dodge Donovan and hand off the File to be leaked out into the world. Although she successfully makes the drop, her contact turns out to be fake, and kills her on the spot, framing her death to look like a suicide. As such, it doesn’t take long for a heartbroken Donovan to figure out that MI5 is behind their own agent’s murder. For the same reason, he quits and decides to go against the organization by leaking the file Alison sacrificed her life for.

As such, Donovan double-crosses the agency after managing to get his team, made up of Alison’s civilian siblings, hired by the Chieftans to run the Tiger Team Operation at The Park. Once he accumulates his hostages, he makes the demand to gain access to the Gray Books since an inside source has informed him that the Footprint File is kept in the same filing facility as the former. Furthermore, after Standish learns about his story, she’s compelled to hand over information about the file since she had helped categorize it.

As a result, after Donovan arrives at the facility with River and Louisa, he makes a beeline for the Footprint File. Nevertheless, around the same time, Ingrid figures out his true mission, and her men, led by Duffy, soon overrun the facility. The Footprint File holds the one secret that has the ability to ruin Ingrid’s career by uncovering a dark secret from her past.

After Ingrid was appointed the head of MI5, she ran an operation in Istanbul, where she signed off on a device’s test run that could tap into encrypted computers wirelessly. Although the device would have been revolutionary for the Service, it ended up malfunctioning, leading to the death of a senior North Korean spy and his soldiers, alongside one civilian. For the same reason, Ingirid ordered a hit on one of her own agents, Alison Dunn, to keep her secret. Likewise, she does the same thing with Donovan and everyone else inside the facility.

Still, even under attack, Donovan continues searching for the file, much to River and Louise’s chagrin. After retrieving the file, the trio tries to make a run for their lives, only to find themselves surrounded. In the firefight, Donovan gets shot in the leg, forcing River and Louise to leave him behind. Yet, he hands the Footprint file to them, divulging the truth behind Alison’s death.

As such, even though Donovan dies, once River and Louise escape from the facility with Shirley and Marcus’ timely help, River makes off with the file. Nonetheless, he remains uncertain about his next move. Thus, he visits his grandfather, David Cartwright, whose remarkable legacy always overshadows River’s own career. Even though David has been losing his memory, he vehemently advises River against blowing the whistle on his superiors and even burns the file to ensure it remains buried.

However, River knew better than to bring the Footprint file to his grandfather without making a copy of it first. Having read through the file, River can’t overlook Ingrid’s wrongdoings, as they resulted in the accidental death of numerous people, as well as Alison’s intentional assassination. Furthermore, the woman even tried to kill him and his colleagues, alongside Douglas, the innocent facility worker. As such, River decides to leak the file’s contents in the end, incriminating Ingrid for her crimes.

Does Diane Get Promoted To First Desk?

While Donovan’s storyline unfolds in the filing facility, a different plot unveils itself back at The Park after Ingrid goes to confront Diana. Ingrid knows Donovan has an inside source to the MI5, who has tipped him off about the Footprint File’s location at Diana’s filing facility. Yet, the Footprint File isn’t actually supposed to be at that facility. Since Ingrid couldn’t destroy the file without leaving a paper trail, she has been moving it around, hoping it would fade into obscurity.

Nevertheless, once Diana learned about it, she transferred it to her own facility. Furthermore, she anonymously orchestrated the entire thing— from the Chieftan’s employment by Judd to Donovan and River’s involvement. It was no secret that Diana was envious of Ingrid’s promotion as the Agency head since she’s been vying for the same spot. Therefore, after Ingrid continued her refusal to step down from the position year after year, Diana decided to take matters into her own hands.

As such, the discovery of the Footprint File and its ability to ruin Ingrid’s career compelled Diana to come up with the whole scheme. Even though Ingrid manages to catch onto it before it’s too late, Diana emerges as the victor after the Slough House agents defeat Duffy and his Chieftan soldiers. Ultimately, by releasing the contents of Footprint File to the public, River ensures Ingrid gets her due diligence and loses her position as Agency head. Naturally, the title ends up going to Diana, who becomes the new head of MI5.

Does Standish Quit?

In this season, Standish has a miserable time, specifically out of all the Slough House members. Even though she realizes her life isn’t in danger early into her abduction and subsequent hostage situation, the position is hardly pleasant to be in. Nevertheless, once she really finds out Donovan’s story and motives, she can’t help but extend a helping hand. Although Standish is reluctant to believe MI5 would ever kill one of their own agents, she doesn’t trust Ingrid’s leadership.

Despite his death, Charles Partner remains a constant source of inspiration and comfort for Standish, who served as his assistant for years. Therefore, after concluding Charles would have stood up against Ingrid, Standish decides to help Donovan in his mission. Eventually, Ingrid sends out her agents to kill Standish as well, but Lamb manages to intervene and rescue her in time.

However, on their drive back to the Slough House, Lamb and Standish get into an argument that spirals out of control. Goaded by Standish’s assertions about Charles’ virtuous leadership, Lamb blurts out the truth about MI5’s former director. Unbeknownst to Standish, Charles was actually a traitor who had been selling information about the Agency to the Russians. Furthermore, the only reason the man hired Standish was so her alcoholism would prevent her from suspecting him.

The final nail in the coffin arrives when Lamb reveals that Charles was actually planning on pinning the entire ordeal on Standish and had prepared a trail for it. As a result, Standish, who has always idolized Charles, refuses to listen to Lamb any longer and announces her resignation from MI5. The show ends with Standish quitting the Slough House.

Read More: Is Slow Horses Based on a True Story?