Plot
Sir Colin Edensor, a retired civil servant, approaches Cormoran Strike and Robin Ellacott's detective agency seeking assistance extricating his son Will from the Universal Humanitarian Church (UHC), an organization claiming to be a benevolent charity but often called a cult. Strike realizes that he once lived at the former commune where the cult’s headquarters are now located, Chapman Farm near Aylmerton in Norfolk, during his transient childhood with his mother and sister Lucy. Lucy confesses to Strike that she was molested there, to his shock. Robin volunteers to go undercover at the current-day Chapman Farm to gather intelligence about the cult and attempt to get Will out. From former cult members they gather information about the cult, which starves and physically exhausts new members as part of indoctrination, and coerces women into complying with all sexual demands.
At Chapman Farm, Robin meets the heads of the UHC, including founder and leader Jonathan Wace; his wife Mazu Wace, who procured Lucy for the doctor who molested her; and Becca Pirbright, sister of former UHC member Kevin Pirbright, who left the cult and provided information to Sir Colin Edensor before apparently committing suicide. Meanwhile, Strike looks into the circumstances of this and other mysterious deaths connected to the UHC, including multiple suicides, and the 1995 drowning of the Waces’ seven-year-old daughter Daiyu, who is now venerated as the "Drowned Prophet" in the UHC's mythology.
Robin finds Will at the farm, and realizes he has fathered a child there, Qing, with a teenaged girl named Lin. However, he rejects Robin’s attempts to get closer to him. Another church leader, Jonathan’s son Taio Wace, shows sexual interest in Robin, which she struggles to rebuff due to the church’s doctrines on sex. Church leaders use demonstrations of apparent supernatural ability as part of church indoctrination and ritual, and dole out harsh punishments to those who question or challenge church teachings. In a barn, she finds Polaroid pictures featuring young people in pig masks performing sexual acts, and is able to smuggle the pictures out to Strike. Under the punishing food and work routines, Robin begins to lose weight and suffer nervous symptoms.
On the outside, Strike misses and continues to struggle with his feelings for Robin, who is dating policeman Ryan Murphy. He is contacted multiple times by a deteriorating Charlotte, his ex-girlfriend, but refuses contact despite her claim that she has cancer. He makes contact with more former members of the UHC, including Jonathan’s resentful adult daughter Abigail, and interviews witnesses to Daiyu’s drowning. He learns of strange behavior by former cult member Cherie Gittins, who was with Daiyu on the beach the day she drowned, but is unable to track her down. He learns that Charlotte has committed suicide after leaving him several voicemails, and struggles with guilt and regret.
After barely escaping sexual coercion by both Taio and Jonathan Wace, Robin is targeted by a jealous Becca and worries that she will be discovered. She builds a rapport with Emily Pirbright, the disgraced sister of Becca and Kevin, who tells her that Daiyu did not drown. Robin then tricks Will into speaking alone, where she reveals the news of his mother’s death a year prior; he reacts angrily and hits her. Robin is punished by drowning in the church’s baptismal pool and then locked in a small box for hours; on release, she is forced to care for a deformed and dying child named Jacob. On being pressured again to sleep with Taio, she makes a run for it, narrowly escaping the grounds with Strike. They report Jacob’s condition to the police, but the UHC moves him and covers it up before he can be found.
The church targets Robin, involving the police and accusing her of molesting Jacob. As she recovers from her ordeal, Robin joins Strike in interviewing Cherie Gittins, who has changed her name and moved to the suburbs. Cherie insists Daiyu drowned, and commits suicide shortly after they leave. Will appears at the detectives’ office with his daughter, having escaped the farm. He initially refuses to contact his family or speak out against the UHC, but begins to recover as the detectives agree to help extricate Lin, the mother of his child. He reveals that Jacob died shortly after Robin's escape. Robin arranges a supervised therapy session between Will and fellow former UHC member Flora Brewster, in which Flora reveals the church's "Divine Secrets", including Jonathan Wace's corrective rape of mentally ill women and lesbians; the burial of unreported dead at the farm; and a large-scale child trafficking operation with the church members’ unregistered births.
Strike and Robin pressure their police contacts and coordinate a crackdown on the UHC’s illicit activities, leading to a police raid of the farm. Robin pursues Becca to the UHC's London temple as Strike confronts Abigail, positing that she murdered Daiyu out of jealousy, disposed of the body using pigs, and faked her death via drowning, with the coerced help of Cherie and other teenage cult members. At the temple, Robin finds Mazu Wace hiding out with a UHC member's stolen baby, and overpowers her, revealing how Daiyu died and Becca’s longtime childhood manipulation after witnessing Daiyu leave the dormitory long before her alleged death.
In the aftermath of the church’s breakdown, Jonathan Wace is arrested, while Becca remains faithful to the now-discredited UHC. Will is reunited with Lin and his family, and they rename their daughter Sally in honour of his late mother. Strike meets with Charlotte's sister Amelia, where they discuss Charlotte's suicide note and last words, finding peace in letting her go. Just as Robin is leaving for a trip with her boyfriend Ryan Murphy, Strike indirectly confesses his love for her.
