In 1960 suburban America, Alice Bradford and Céline Jennings are next-door neighbors and mothers to boys of a similar age. Alice stages a surprise party for Céline's birthday. The next day, Céline's son Max stays home sick from school. Alice, pruning roses in her own garden, spots him standing precariously on a balcony, trying to hang a birdhouse he made at school. Alice, realizing the danger, tries to crawl through a small tunnel-like break in the hedge separating the two properties but her large sunhat prevents her from doing so quickly. She then runs around the hedge to reach the front door and attempts to alert Céline, who is inside vacuuming. The two are unable to act quickly enough and Max falls to his death. After Max's death, Céline distances herself from Alice, but grows closer to Alice's son, Theo. At Max's funeral, Theo notices one of his own toys in Max's coffin and lashes out. After the funeral, Céline leaves for an unknown location for a month, and when she returns, she reconciles with Alice. One day, Alice leaves Theo with Céline at her house and she sees Theo playing with
bubbles on the same balcony Max fell from. She panics and runs to him, but this time she crawls through the passageway in the hedge and immediately gets near Céline's house. Céline appears beside Theo, explaining she was watching him, but she quickly noticed Alice could get through the hedge for her own son, unlike the last time for Max. Alice also notices that and thinks the incident was Céline's attempt to test her. Theo grows even closer with Céline, to the point of inviting her to his birthday party, much to Alice's dismay. The party goes as expected, but afterward, Alice's mother-in-law (Simon's mother) suddenly collapses, dying of a heart attack. Simon's mother has been taking medication for her heart, but an autopsy carried out at Alice's request reveals no trace of that medication in her bloodstream. Alice suspects that Céline has been replacing the drug with a
placebo, but her attempts to find evidence prove fruitless. Alice's suspicions deepen when Theo is hospitalized after a severe allergic reaction at Céline's, with her believing Céline has deliberately encouraged Theo to eat food to which he is allergic. Alice enters Céline's house while she is out one day to attempt to find evidence, but Céline catches her and orders her to leave. Alice and Céline, eventually reconcile after Theo threatens to take his own life in response to their feud. Simon finds a house so their family can move away from Céline, and Alice breaks the news to Céline. Later that night, Céline kills Damian, her husband, by sedating him with
chloroform and slicing his wrist, making it look like a suicide. Alice and Simon allow a seemingly distraught Céline to stay with them. However, while Alice goes to Céline's house to gather the rest of Céline's things, Céline sedates Simon and Theo. When Alice discovers this, the two women fight. Alice initially fends off Céline's attempt to forcibly sedate her, but Céline later succeeds. She kills both her and Simon by disconnecting their boiler to stage a gas leak. She spares Theo and later adopts him. ==Cast==