In Gloucester in February 1994, social worker Janet Leach Emily Watson serves as an appropriate adult during police interviews with vulnerable individuals. She accompanies Fred West Dominic West to a session where he confesses to the 1987 murder of his daughter Heather, a revelation that shakes the case to its core. Fred privately hints that there were more victims, but the rules around appropriate adults prevent any sharing of such conversations. As investigators uncover the remains of several women buried at the West home, Fred names Shirley Robinson, a lodger killed in 1978 while pregnant with his child, as one of the victims.
Janet is given the option to step away from the distressing case, yet she resolves to press on. West tells the police there is a third body in the garden, and DC Hazel Savage Sylvestra Le Touzel grows wary that Rena West, Fred’s first wife, and Charmaine, his stepdaughter who disappeared in 1971, may also be buried there, with Fred denying Rose West’s involvement. Fred seems startled to learn that Shirley’s baby was removed from her abdomen, suggesting Rose Monica Dolan might have taken it.
As the investigation deepens, Fred expresses to Janet that they share a strange connection. Disgusted, she contemplates stepping away, but he pleads for her to stay, and she agrees on the condition that he fully confess, which he does, admitting to “approximately” nine murders. Police begin to dig in the Wests’ basement and in the Herefordshire countryside, while Fred redirects Janet toward another site and recalls his “true love,” Anna McFall. DSI John Bennett Robert Glenister worries that the confession could have been coerced or crafted to impress Janet and warns her not to become too entangled.
The case draws media attention, and Janet’s partner Mike Anthony Flanagan, who is bipolar, urges her to sell her story. He experiences a manic episode and is admitted to hospital, straining their relationship as their son Josh Rupert Simonian accuses Janet of neglecting the family. Fred reveals that he and Rose agreed to him taking the blame so Rose could look after the family, even while he calls Janet “Anna” and suggests they are bound for a shared journey.
Evidence of additional victims emerges as the search continues, and Fred leads investigators to a rural location where he claims to feel Anna’s presence, insisting she is guiding him. Savage confirms that Anna was Fred’s teenage babysitter during his marriage to Rena and that they had an affair, after which Anna disappeared.
Eventually, Fred and Rose are charged with murder, and Savage tells Janet she is no longer needed. Janet’s family life resumes until Fred phones from prison, requesting her help locating a solicitor, much to Josh and Mike’s dismay. A twelfth body is identified as Anna, and with Janet’s help, Fred begins drafting a memoir.
A journalist friend suspects ritual killings may be part of the Wests’ crimes, and Janet’s collaboration with Fred continues to draw scrutiny. Fred speaks of hearing the screams of children in a barn and claims there were many more victims—perhaps twenty or more—though Janet’s faith in uncovering the full truth remains fragile. When Janet cancels a Christmas visit, Fred calls again, claiming he sees more of Anna in her than in Rose.
Self-destructive patterns surface as Fred ultimately hangs himself in prison. With the duty of confidence no longer in effect, Janet recounts all that Fred told her. Bennett dismisses the idea that the book Fred wrote matters and tells Janet that she meant little to him. Back home, Mike catches Janet preparing to swallow pills, and she admits she misses feeling needed and important.
In court, Janet testifies that Fred described Rose as sadistic and murderous, then falsely swears she never spoke to the media about the case, only to collapse under pressure. Reappearing in court, she admits selling her story and Alvarez-like scrutiny follows: the defense accuses her of egging Fred on to invent lurid tales and hints at a romantic connection. She maintains she sought the truth, and Rose is found guilty and sentenced to life in prison. A journalist discovers a barn location that matches Fred’s description, but Janet remains unsure that the entire truth will ever be known, choosing to return to family life despite the haunting memories.
