Emergency lights strobe outside a Beverly Hills house as a police officer named Ethan questions Brooke Lyons, a new mother who had been attending a party at the house, in a bedroom. A detective named Perez takes over and notes Brooke’s calm, asking if she has medical training. When Perez mentions multiple bodies, Brooke corrects her, saying that there is a single body. Brooke feels numb, believing an unspecified past trauma has prepared her for anything.

A flashback reveals the events that led to Brooke’s questioning: She heard a scream and ran outside to see Kiersten McCann, the hostess of a party Brooke was attending, floating face down in the house’s pool. The image is fixed in her mind as she tells herself that her composure is a result of having already lived through the worst thing imaginable.

As officers lead Brooke from the room, Whitney Gilmore, Kiersten’s best friend, lunges at her, screaming words of blame. Another partygoer, Jade Porter, pulls Whitney back, and an officer then escorts Whitney to a guest bedroom. Detective Perez questions Whitney, who explains that the party was a “night out” for their exclusive club, the “West Hollywood Moms’ Club.