In the present, Helen Lingate reflects on her family’s wealth and how having too much or too little money makes her anxious. She reveals that the family’s origin story, that her great-grandfather struck oil while prospecting for gold, is a lie created to hide the truth that he swindled a widow out of an oil lease. He promised to split the profits if oil was found within five years, then he delayed drilling until five years and one day later. While her mother Sarah’s death 30 years ago tarnished the family myth, Helen sees it as a story she can now use to her own advantage. Waking up hungover in a bed she shared with her boyfriend, Freddy, Helen goes to check on her friend, Lorna Moreno. She finds Lorna’s room empty and the bed untouched, and questions whether the story she and Lorna told each other was the truth.

Lorna is on a chartered yacht traveling to Capri with her employer, Marcus Lingate; his wife, Naomi; his brother, Richard; Richard’s daughter, Helen; and Helen’s boyfriend, Freddy. Marcus tells Lorna, his assistant, that she is on vacation and should not work, a claim she finds hard to believe. Although Marcus arranged Lorna’s flight, Lorna chartered the yacht, booked the villa, and made all other arrangements for the Lingate’s annual trip to Capri. When the yacht was late, Marcus instructed Lorna to get them a refund. As she reflects on her friendship with Helen and the lingering questions surrounding Sarah Lingate’s death on the island, the yacht docks at the Marina Grande. During the process, the captain’s hand is crushed between the boat and the dock. The Lingates disembark with indifference, while Freddy passes Lorna a wad of euros, which she holds until the stewardess pries them from her fingers.

On the dock, Marcus praises Lorna for her composure around the captain’s injury, noting that Naomi cannot stand the sight of blood. As they travel by taxi to the town of Capri, the group encounters Stan Markowitz, a family acquaintance. Marcus is cold toward Stan, who says he will call Lorna to arrange a dinner. Lorna recalls a prior incident when Stan visited Marcus’s office, angrily insisting the Lingates got away with Sarah’s murder. The family arrives at their villa, and as the gates close, Lorna is overcome with a feeling of being trapped.

Returning to the present, Helen finds Lorna’s room empty and feels foolish for trusting her. She remembers her father’s warning to only trust family. In college, Helen gave a confidential interview to a writer named Alma about her mother’s death, thinking Alma could be trusted. Alma then tried to publish Helen’s story, even though Helen wanted it to be off the record. When her family found out, they used their influence to kill the story and pulled Helen from school. When they allowed Helen to return, they subjected her to intense surveillance. The experience taught her that she had to learn to follow her family’s rules to survive. Helen puts on a gold snake necklace and goes downstairs to face her family, knowing everyone is waiting for Lorna.

Lorna watches as a housekeeper delivers a package to Helen at the villa. In her room, Lorna hides an envelope under the mattress before running into Freddy in the hallway. He wants to tell Helen about his and Lorna’s past in the party scene in LA, but they decide to keep it a secret from Helen for the week. In the garden, Helen opens the package and finds a gold snake necklace that belonged to her mother, Sarah. Richard is stunned, confirming the necklace is authentic and was lost at sea when Sarah died. As the family reacts with fear, Marcus pockets the note that accompanied it. Both Lorna and Helen already know what the note contains and watch the family’s reaction. The housekeeper carrying Lorna’s lemonade drops the glass in the commotion. When Lorna tries to help clean up, Naomi screams at her to sit down.

Helen finds Richard, Marcus, Naomi, and Freddy having breakfast by the cliffs. She tells them Lorna is missing, explaining that her bed wasn’t slept in and she never came home. The family is dismissive, offering excuses that Lorna met a man or that her phone died. They ignore Helen’s suggestion to stay at the villa’s pool and decide to proceed with their scheduled boat trip for the day.

The group eats at a restaurant, and Lorna reflects on the motivation behind her and Helen’s plan. She recalls a hike at Runyon Canyon where Helen revealed that Richard illegally liquidated a trust fund of $2 million that Sarah had established for Helen. Richard had been the named trustee until Helen turned 30, but he drained the account while she was still in school. The family lawyer, Bud, had Helen sign an indemnity agreement, forcing her to promise not to sue for malfeasance. Trapped and financially dependent, Helen told Lorna she was determined to get out of her family’s control but needed to leave with enough money to survive.

As dinner continues, Naomi makes pointed comments about Marcus’s past “indiscretions” and accuses the deceased Sarah of “stealing” ideas for her plays. Lorna notes that Naomi has been drinking heavily on Capri, and she sees Marcus move a bottle of wine away from her. During the meal, Stan texts her that he has the money and is waiting for her to give him something. Lorna excuses herself to the restroom and steps into an alley for a cigarette. There, a waiter from their table approaches her and calls the Lingates “killers,” adding that everyone on the island knows their history.

A newspaper article from July 20, 1992, reports that Sarah Lingate’s body has been recovered by fishermen from an inlet near the Faraglioni, a rock formation off Capri. Her body was badly damaged but identified by clothing and wedding rings. The article states that local authorities do not expect to name a suspect, as preliminary findings suggest the death was either accidental or self-inflicted. It also notes that the Lingates’ three-year-old daughter, Helen, was in Los Angeles with a nanny at the time.

Sarah lounges by the villa pool with Richard, Marcus, and Naomi. They are all hungover, and Sarah reflects that it will be her last summer in Capri.  Richard pressures Naomi and Marcus to have children, and Sarah knows Richard wanted a child to feel more “adult” than Marcus. Sarah alludes to a “new” play she has written that the family has suppressed. When the conversation gets heated, Sarah leaves to sit with Renata. She overhears a heated argument between the brothers in which Marcus shouts that Richard is not handling Sarah well, which puts the family at risk. Renata warns Sarah not to  let the family control her. The chapter also mentions Renata’s young son, Ciro, whom Sarah hopes will play with Helen.

Lorna is at a beach club with Helen and Freddy. Lorna remembers when she and Helen found the snake necklace, which was  anonymously mailed to Marcus’s office. Helen and Lorna verified its authenticity and decided to send it on to the villa in Capri to use as leverage against the family. In the present, Helen and Lorna swim to a secluded area across the bay. Helen confesses she believes the family psychologically pushed her mother toward an accident or death by suicide. Ciro interrupts their conversation and offers to bring them to shore on his boat. As they board, outnumbered by the men, Lorna feels nervous.

Twelve hours after Lorna went missing, Helen and Freddy are on a boat trip with Ciro. Helen reflects on her romantic relationship with Ciro, which began when they were teenagers. Helen spent a year in Rome after the situation with Alma, during which Ciro lived with her for a month. They visited Naples together, where Helen said she could see herself moving to Italy. While swimming, Freddy tells Helen he needs to confess something about Lorna. He reveals that he knew Lorna from the “party scene” long before Helen introduced them. Helen is surprised that Lorna kept a secret from her, but she feels their shared secret is more important. He says Lorna can take care of herself and asks Helen if she thinks Lorna was involved in the appearance of the necklace.