‘Slow Horses’ Season 3 Ending Explained & Finale Recap: What Happens To Diana And Ingrid?

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Season 3 of AppleTV+’s spy thriller series Slow Horses comes to an action-packed end with the season finale episode this week, with all of the matters brought to a final resolution. Like every other time, though, there is a sense of loss even though goals have been reached and missions have been carried out just as planned. Along with presenting a thoroughly entertaining and thrilling story in the third season, Slow Horses also develops some of the beloved misfit spy characters from Slough House and is an absolute must-watch for fans of the show or even the genre.

Spoiler Alert


Plot Summary: What is season 3 about?

Slow Horses season 3 began with a very personal crisis for the Slough House members, for Catherine Standish had been kidnapped by a rogue group. When River Cartwright made all attempts to save the woman by breaking into the MI5 Regent’s Park headquarters and stealing a file that the kidnappers wanted, it all turned out to be just a ruse. The kidnapping, and the subsequent break-in by River, were all part of a plan to undermine the MI5’s hold over the internal security of the nation, and to make way for private security firms into the role. The Home Secretary, Peter Judd, had appointed his friend, Sly Monteith’s security firm, Chieftain, to carry out the whole plan, as part of a secret pact made with Diana Taverner, in order to put MI5 Director-General, Ingrid Tearney’s career at stake.

However, while Judd thought he was working with Taverner, the MI5 second desk was actually using him too, in order to achieve her very personal desire to become the DG. Taverner wanted to take Tearney’s job, and she did not only stage the breach of security at MI5, but she had also appointed a very special Tiger team, led by ex-MI5 agent Sean Donovan, to get hold of a file that would surely get Tearney fired. The file contained information about how Tearney had launched a secret mission to remotely hack into enemy computers, which had terrible effects on a number of innocent civilians and spies. An agent named Alison Dunn had wanted to expose this file, and the secrets of Tearney’s failure, and so the MI5 head had gotten Alison killed in Istanbul. Sean Donovan happened to be the grievous ex-lover of Alison, and as soon as he was contacted by Taverner, the man jumped in to get revenge against his lover’s unjust murder. 

At present, Tearney had ordered for Donovan and his associate, Ben, to be granted access to the confidential MI5 archive facility. She had also appointed River to oversee this mission, but as soon as Tearney learnt that Donovan was looking for the file that would bring her down, codenamed Footprint, she changed her orders. Sending the Dogs tactical unit and the Chieftain militia to the place, the MI5 head called for the execution of Donovan, and everyone present at the place. Slough House agent Louisa Guy had accompanied River to the mission, and when they called for help, Shirley and Marcus had also arrived at the facility, amidst heavy gunfight. On the other side, Jackson Lamb had gone to rescue Catherine, when a car rolled up onto the driveway, posing great danger for the two agents.


Can Lamb rescue Catherine?

When Jackson Lamb spotted the car arriving in front of the Dunn house, he figured out that it must have been sent by the MI5 to get rid of Catherine. While on his way to the place, the Slough House leader had received a call from River, and from this conversation, he had understood that the MI5 higher-ups had ordered the killing of his agents. Therefore, Lamb preps the entire house to look like nobody’s inside, making Catherine hide inside a closet, while Sara is sent upstairs along with a gun, and Lamb himself prepares for an ambush attack. The man also sets up various booby traps across the house, both to harm the intruders and also to understand their movement patterns, and all of this works to great benefit. 

The intruders were indeed there at the house to find and kill Catherine, for they were Sturges, the Chieftain operative, and Hobbs, the MI5 henchman. As soon as the two enter the house where Catherine had been kept hostage, which was actually Sara Dunn’s house, they have to face the traps set by Lamb. Eventually, Sturges is able to spot Sara and shoot at her, but the woman also fights back and manages to choke him to death. As an injured Hobbs walks up to the closet where Catherine was hiding, he is also shot dead by Lamb, ensuring that there is no more danger to them for now.

The Slough House hacker and tech specialist, Roddy, had also been near the place, as it was he who had driven Lamb there, and when he spotted another car arriving, Roddy had decided to investigate. Realizing that his colleagues were in trouble against the intruders, especially since there were gunshots inside the house, Roddy stepped in by starting up an old bus and ramming the vehicle into the side of the house, intending to kill the bad guys using this technique. Roddy’s heroics naturally do not help, for Sturges and Hobbs have already been put down by then. Lamb, Catherine, Sara, and Roddy now drive away from the place, dropping Sara Dunn off at the hospital to get her injuries checked, as Catherine had become friends with the woman by now.

As the three Slough House agents drive away from the hospital, they discuss the ongoing situation, and Lamb confronts Catherine about why she had helped the Tiger team. The woman makes it clear that she has a number of issues with Tearney-led MI5, and therefore, she was convinced by Donovan’s claim that the service had killed his lover. The elderly woman compares Tearney’s leadership with that of her earlier boss, Charles Partner, calling his time as the MI5 head to be extremely good and glorious. While Jackson Lamb had maintained his silence over this matter for so long in the three seasons of Slow Horses, the man finally reveals the real truth.

Catherine had genuinely been believing a lie about Partner being the best MI5 leader, for the man had actually worked as a foreign spy during the latter half of his career. When Catherine still defends her former boss by stating how he cared for her unlike anybody else, Lamb clarifies that this was because Partner needed an assistant who would be drunk and careless most of the time, and Catherine fit into this role very well. In fact, Partner was staging his entire betrayal to make it seem like it was his assistant, Catherine Standish, who was the real double agent. It was because of other MI5 agents, like Lamb himself, that Catherine did not get into any such trouble. Lamb even suggests that Catherine always knew about this real truth, but she simply lived in denial, out of her love and admiration for Partner. This confrontation does not go down very well, and Catherine immediately walks away from her colleagues, announcing that she is quitting Slough House and MI5 at this very moment.


What happens to the Slough House agents at the archive facility?

Back at the confidential MI5 archive facility, which was just an old Cold War-era bunker, River and Louisa are in great trouble as their room is infiltrated by a Chieftain soldier. But Sean Donovan, who was once a very effective security service agent, manages to get hold of a rifle and shoot down most of the soldiers. After spending a few moments recovering from the impact of the grenade, River manages to get up, unlike Ben, who had been shot dead at the end of episode 5. As soon as Donovan is able to kill enough soldiers for them to fall back, the three escape the room since there is no reason for them to hang back.

Donovan had secured the Footprint file and was carrying it very safely with himself, with the intention of leaking the file to the public and exposing Ingrid Tearney’s scandalous acts. But in the process of making their way towards the only hatch to escape the facility, the group has to face heavy gunfire, and Donovan gets shot. Although the wound does not immediately kill him, it definitely slows him down, leading to Donovan taking a crucial decision. He hands over the file to River, asking him to safely take it out of the facility and hand it over to the right authorities, while he decides to stay back and keep off the soldiers for some time. The plan does work for some time, as the man is able to divert the attention of the Chieftain soldiers, but ultimately, Sean Donovan gets shot dead by a soldier. Therefore, by the end of Slow Horses season 3, Sara Dunn is the only individual among the rogue Tiger team to have survived the ordeal, while her brother, Ben, and Sean Donovan are dead.

River and Louisa are still chased by the Chieftain soldiers, and they have to make their exit through the hatch, but the place is also heavily guarded by three soldiers placed by Nick Duffy. It is now Shirley who comes to their rescue, as she and Marcus had already been fighting off soldiers at another spot in the facility. The two get into tricky situations, but both are able to get out of them, and as Marcus has to face Duffy himself, Shirley takes her colleague’s car and races to the escape hatch. She takes down the soldiers at the place and then helps River and Louisa get out of it. Shirley also lovingly leaves behind a small gift for the remaining soldiers down the hatch—a live grenade, which kills them instantly. Some heated words are exchanged between Marcus and Duffy, as the former had once been offered a job in the Dogs tactical unit, but the man had chosen to be a Slough House agent instead. This was because Marcus knew how insensitive a leader Duffy was, and he had no desire to work under him. Ultimately, when Duffy is about to hurt Marcus, Louisa Guy steps in and helps her colleague, balancing out Marcus’ favor from the end of season 2, when he had saved Louisa from death at the hands of Arkady Pashkin.


What happens to Diana Taverner and Ingrid Tearney?

As the two women at the top of the MI5 administration sit and wait for the events at the archive facility to unfold, they still put faith in their respective sides. While Taverner believes that the resolute Slough House agents will prevail, Tearney is confident that the more professional tactical team and Chieftain soldiers will manage to secure her position. The ultimate result favoring either of them would immediately mean that the other would be harmed, and the two women look onto the battlefield like generals who have put out their armies to fight. In the end, as the media starts picking up on the news of this shocking gun battle, it is evident that Tearney’s side has lost, and Nick Duffy cannot be reached on the phone either.

However, the extent of Tearney’s loss would depend on what happens with the Footprint file, and so River takes it to the most trusted help he believes he has—his grandfather, David Cartwright. The retired MI5 officer had been earlier seen in Slow Horses season 3 when it was revealed that he was losing his memory. When David listens to the entire matter and goes through the Footprint file, he makes the obvious decision to not reveal anything about it to anyone. After all, the man had himself been a part of many MI5 internal killings, as he was the one to order the execution of Charles Partner. Therefore, he states that leaking the Footprint file will only cause more trouble, especially for his grandson, and so David burns the file down. It seems like the man is scared that River will also be hunted down by the MI5 if he brings down Tearney, but David perhaps does not know the plot that Diana Taverner is in control of.

Despite always being very dedicated and respectful towards his grandfather, River, too, had started to feel that David’s intuition and judgments could not be blindly trusted anymore. This realization had also grown on River after the events of season 2, in which David had known about the cicadas but did not tell his grandson anything about them. As a result of all these learnings, River Cartwright had gotten a copy made of the Footprint file before he went to David, and so, even though the senior MI5 retiree burns down the original, the file and its contents are still technically safe and ready to be leaked. This is exactly what happens, as River Cartwright leaks the photocopied file, which leads to Ingrid Tearney finally being put away for good. As expected, it is Diana Taverner who takes her spot and moves up to the rank of MI5 Director General. The Home Secretary, Peter Judd, is also removed from office immediately, because of his involvement in the whole matter.

Slow Horses Season 3’s ending revealed the entire mystery in a scene in which Taverner and Lamb meet once again. He reveals that leaking the file was entirely River’s doing, and surely Taverner would protect the spy from any danger in exchange for this great favor. The season ends with Lamb talking about how Taverner had risked the lives of so many people only for her promotion, but the woman is unfazed, as, according to her, it was all Tearney’s doing. Lamb agrees to disagree and walks away from the place, making it clear that being distant from such horrific decisions of the MI5 administration gives him a lot of peace as the leader of the neglected but effective Slough House.


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Sourya Sur Roy
Sourya Sur Roy
Sourya keeps an avid interest in all sorts of films, history, sports, videogames and everything related to New Media. Holding a Master of Arts degree in Film Studies, he is currently working as a teacher of Film Studies at a private school and also remotely as a Research Assistant and Translator on a postdoctoral project at UdK Berlin.

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