Nel Abbott’s death precipitates her sister, Jules, coming back to Beckford. Everyone in the town has strong feelings about Nel’s death, with some, like her daughter Lena, deeply upset and others glad to see her gone. Jules meets Lena, who insists she knows what has happened to Nel. Lena is also upset over the recent death of her best friend, Katie, who died, like Nel, in a local pool of water called the Drowning Pool. Detective Inspector (DI) Sean Townsend and Detective Sergeant (DS) Erin Morgan lead the investigation into Nel’s death.

At Nel’s funeral, Jules sees Robbie Cannon, Nel’s high school boyfriend who raped Jules when she was 13. As with her death, reactions to Nel’s funeral are varied. The Whittakers—Katie’s family—decide to leave town to get away from the feelings surrounding Katie’s death. While cleaning Katie’s room, her mother, Louise, finds diet pills prescribed to Nel and goes to the police, believing that Nel must have been responsible for Katie’s death. Lena reveals that she bought the pills for herself but recalls that Katie had a sexual relationship with her teacher Mark Henderson, who has now left town. Lena and Katie’s sister, Josh, break the windows at Mark’s house in revenge for his driving Katie to her death.

Josh, unable to continue repressing what he knows, reveals Katie’s relationship with Mark to DI Townsend. Sean and Erin question Lena, who tells them that Katie killed herself to protect Mark. Louise confronts Lena over her knowledge of Katie’s relationship with Mark. Lena tells Jules that Nel scared or threatened Katie and drove her to suicide; she then runs away from home and goes back to Mark’s house. Mark finds Lena there. They fight, and Mark drives out of town with Lena in his trunk.

Jules realizes that Lena is Robbie’s daughter and goes to confront him. She learns that a key fact she believed about Nel—that Nel knew of her rape—was untrue, and this reframes her whole relationship with her sister. Meanwhile, Erin learns that Sean was romantically involved with Nel, which calls his involvement in the investigation into question.

Mark drives Lena to a seaside cottage. They fight, and Lena likely kills Mark. Lena shows up in a nearby village and Sean brings her back to Beckford. Lena tells Jules that Nel was murdered, having learned from Mark that Helen Townsend, Sean’s wife, had a bracelet in her office that was missing from Nel’s body after her death.

Jules goes to the Townsend house and accuses Helen of murdering Nel. Patrick then confesses to killing Nel and to killing his own wife, Lauren, years ago.

In the months after Patrick’s confession, each of the characters leaves Beckford. Jules and Lena go to London and have a much stronger relationship than they did at the beginning. Patrick is in jail. Helen and Sean leave together, but Sean disappears one day and Helen does not look for him. Sean, in an undisclosed location, tries to come to terms with himself and admits that it was he who killed Nel.

Woven through the narrative excerpts from a book Nel was working on—The Drowning Pool—which purported to tell the stories of various women of Beckford who were drowned, killed their husbands, or were somehow involved with the Drowning Pool. These women include Libby Seeton from the 1600s, Anne Ward from the 1920s, Katie, Lauren Townsend, and Nel herself the night she saved Jules from drowning just after Jules’s rape.