[1] Sir Colin Ensor, 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), which has been deemed a cult by critics but claims to be a benevolent charity.

As Strike reads about the UHC, he realises that it was formed on the site of a 1960s to 1980s commune, the Aylmerton Community, where his transient mother Leda briefly brought him and his half-sister Lucy to live in childhood.

When he mentions it to Lucy, she reacts intensely negatively, finally revealing that she was sexually assaulted as a child by the farm's doctor after being procured for him by Mazu, an older girl who is now one of the UHC's leaders.

While hiding in a barn, she finds Polaroid pictures featuring young people in pig masks performing sexual acts, and puts them in the rock the following week.

After waking in a hotel near the beach where Daiyu drowned, having interviewing people who witnessed the event the day before, Strike learns that Charlotte has committed suicide.

That evening, after Jonathan Wace commands her to have sex against her will with his son Taio, Robin runs for the blind spot where Strike is waiting, having not received a message from her that week and found the hollow rock missing.

Strike and Robin interview former UHC members including Carrie Curtis Woods, as Cherie Gittins is now known, who insists Daiyu Wace drowned when she took her to the beach.

Pat and her husband Dennis volunteer to care for Will and Qing at their house while Midge and grateful client Tasha, who have begun dating after her abduction case was closed, find Lin at Dr. Zhou's medical centre near London and try to release her.

Robin arranges an interview between Will and fellow former UHC member Flora Brewster, who convinces Will that the Drowned Prophet, whom he still fears, is not real when she reveals the church's "Divine Secrets" without dying - Jonathan Wace's corrective rape of mentally ill women and lesbians, the burial of unreported dead at the farm, and a huge-scale child trafficking operation.

Strike breaks the news the police have raided Chapman Farm and the Birmingham centre, which was used as a base for trafficking surplus babies born to UHC members.

In the epilogue, Jonathan Wace has been arrested trying to drive across the United States border into Mexico, Mazu insists that she is still the mother of the Drowned Prophet despite all evidence to the contrary, and Becca remains faithful to the now-discredited UHC.

[2] Joan Smith, writing in The Times, says the book reveals Rowling's "extraordinary resilience" to remain in the public eye after suffering "vicious abuse", and also shows her "intense sympathy for the underdog".