The title “Daddy Issues” seems like an obvious reference to River Cartwright and Frank Harkness. And it is, of course. River has just buried the grandfather who raised him as a son and, on the same day, encountered the biological father who abandoned him, turned his other sons into soldiers and, last season, placed a grenade in his hood. It would be enough material for years of therapy. Yet the second episode of Slow Horses Season 6 broadens the issue: there is also a child who witnesses his own father’s murder and is immediately treated as one more loose end. Fathers, sons and the damage left between them are at the center of a conspiracy that is finally beginning to take shape.

The episode opens by revealing what brought Frank back to London. Andrew Nesmith, a recently dismissed former Dog, was hired to remove a file from Molly Doran’s archives. He was caught somewhere he was not supposed to be, but no one realized that the document itself had disappeared. When he loses his job and tries to demand more money for the service, however, he becomes a liability. Frank strangles him and stages the scene to make his death look like suicide.

The plan would have worked perfectly if Andrew had been alone. His son, Reece, was in the house and managed to escape. Frank eliminated one witness but created another, and this time it is a boy who has moved between foster homes and is now missing, knowing that someone murdered his father.

Meanwhile, River is obsessed with Frank. This is not merely a professional investigation, no matter how much he tries to treat it as one. His father’s appearance at David’s funeral was a carefully calculated provocation, and River, still drowning in grief, is in no emotional condition to ignore it. He asks Roddy to track Frank’s rental car, leading him and Lamb to Andrew’s house.

The scene looks like a suicide, but Lamb immediately realizes that something is wrong. Money, cards, a phone and a computer are all missing. River spots a security camera on the building across the street and discovers from the footage that a child was at the scene. Roddy identifies the boy as Reece Nesmith. Frank later confirms the existence of a “minor complication,” an especially cruel choice of words for a kid who has just watched his father being murdered.

Lamb, however, continues to look at the larger picture. Struan Loy was burned alive inside a shipping container, and Kay White died on the boat where she lived. Both were former members of Slough House. Shirley and Coe are sent to Kay’s boat and find very little, apart from some money that Shirley decides to pocket because, after all, Kay will no longer need it. A local food vendor, however, remembers seeing a man and a woman leaving the boat on the night of her death. Kay did not die by accident. Jim and Jane are working their way through a list.

Their next victim is Moira Tregorian. Pretending to investigate a gas leak, the two enter her home, incapacitate her and fill the house with gas, arranging another death to look accidental. It is a particularly sad farewell for a character who managed to escape Slough House and return to the Park, only to discover too late that no one ever truly stops belonging to that list. Moira’s death also confirms that the killers are not targeting only the current agents. Anyone who has ever been part of Lamb’s team may be in danger.

Diana Taverner is facing a trap of her own. Peter Judd finally introduces her to the man behind the money he gave MI5: Damien Cantor, a businessman and the owner of a right-wing television channel. The money, naturally, was never a disinterested donation. Cantor wants Diana in front of the cameras, and Judd makes it clear that she is in no position to refuse.

The interview begins uncomfortably and quickly turns into a disaster. Diana is questioned about chemical-agent attacks on British soil, possible retaliation operations and rumors that a former First Desk worked for a foreign power. This is information that should never have reached a television presenter. Even Claude Whelan resurfaces by text message to savor his successor’s humiliation.

The most important revelation comes later: Damien was the man who hired Frank to obtain the secret file. Harkness, therefore, did not return solely to torment River, although he probably considers that an additional benefit of the job. He is working for a rich and powerful man with terrifying access to MI5 secrets.

Lamb visits Molly Doran and finally discovers what was stolen: the physical records of every person who has ever worked at Slough House. The digital files were erased from the system, and the paper documents have also vanished. Someone now has the names, addresses and histories of former and current Slow Horses. Struan, Kay and Moira were not randomly selected victims. They are the first names being crossed off a list.

This is when Lamb does what he always does once he realizes his agents are in danger: he stops using insults as his only form of leadership and begins protecting them. He orders everyone to switch off their phones, disappear and meet near William Blake’s grave, the designated emergency meeting point. Catherine goes with him, although their relationship remains frozen after she discovered that Lamb killed Charles Partner on David Cartwright’s orders.

Everyone obeys except River. Throughout the episode, he receives silent phone calls and becomes convinced that Frank is playing with him. Roddy eventually traces the calls: they are coming from David’s house. It is the perfect bait. River has just lost his grandfather, has not even begun to organize his grief, and now believes that his father has invaded the most intimate place in his personal history. Ignoring Lamb’s orders, he rushes there. But Frank is not the person River finds inside the house. It is Sid Baker.

Sid was shot in the head in the second episode of Season 1. River was still able to visit her while she was in a coma, but her records later disappeared from both the hospital and the MI5 system. Lamb told him she had died, although the absence of any documentation already suggested that this was not the whole truth. Five seasons later, Sid is alive, standing in front of River and hiding in David Cartwright’s house.

The trailer had already revealed Olivia Cooke’s return, but that does not diminish the power of the reunion. Within the story, River has just discovered that yet another certainty in his life was built on a lie. His grandfather is dead, his father has returned, Lamb concealed the truth and Sid, whose supposed death has haunted him since the beginning of the series, has reappeared in the place he still associates with the only family he ever truly had.

“Daddy Issues” begins by organizing a conspiracy and ends by unraveling River. Frank stole a list, Damien Cantor knows far too much, assassins are eliminating the Slow Horses, and Reece is in danger. Yet the image that remains is Sid, alive in David’s house. In Slow Horses, the dead never disappear completely. Sometimes, it is because the secrets they left behind continue to destroy the living. And apparently, sometimes it is because they were never dead at all.