The Lingates take a boat to the Li Galli archipelago for Werner Leipling’s party. The family lawyer, Bud Smidge, has already informed them that DNA evidence in Lorna’s murder was inconclusive, clearing the family. Bud dismisses the reopening of Sarah’s case as a political maneuver, and Helen notes that Richard seems more comfortable. 

At the party, Stan finds Helen and passes her an envelope containing her copy of Saltwater. Helen also sees Renata, Ciro’s mother, working at the event, and observes Richard experience a shock of recognition when he spots Renata across the garden. As the ballet is about to begin, Helen approaches Richard and hands him the play.

During the ballet, Helen confronts Richard with the play. She accuses him of murdering Sarah because of her affair with Marcus, but Richard insists he never knew about it. He confesses the family has been secretly bankrupt for decades, living off Naomi’s fortune after his father squandered their inheritance. Sarah had demanded a divorce, which would have exposed their financial ruin when the Lingates could not follow through on the payments required by their prenuptial agreement. Richard claims Sarah fell and hit her head on a rock. Believing the sound of the impact meant she was dead, Richard fled without checking on her.

Helen points out that Sarah’s body was found below the villa, not in the garden where he claims she fell. Richard admits Marcus helped him move the body and stage it as a death by suicide. Helen tells Richard he didn’t fully read the play, pointing to the affair it depicts and asserting that Marcus may have killed Sarah. Richard insists he read enough but cannot account for what he did not know.

Naomi finds Marcus with Sarah’s unconscious body in the garden. Sarah is still alive. Consumed by jealousy over their affair, Naomi wants Sarah dead and retrieves a knife from the kitchen. She overhears Marcus whispering apologies to Sarah and realizes he still loves her.

Naomi confronts Marcus, who admits to the affair but swears it is over. To prove his loyalty, Naomi wants to watch him kill Sarah. Marcus carries Sarah toward the cliffs, but they are interrupted when Richard calls out his name. Marcus goes back to the house to handle Richard, leaving Naomi alone with Sarah. When Sarah begins to stir, Naomi attempts to lift a large rock to kill her but finds it too heavy. Instead, she shoves Sarah over the low stone wall and down the cliffs.

After the ballet, Richard confronts Marcus with Saltwater. Marcus confirms the truth of the play. Naomi emerges from the shadows and reveals to Richard that Sarah was still alive after he fled the garden. She shouts that Sarah and Marcus were having an affair and that Marcus is Helen’s father, allowing people in the audience to hear her. Richard is devastated, realizing Marcus let him believe he was a murderer for three decades to conceal the affair.

Richard attacks Marcus. Other guests try to intervene, and in the ensuing brawl, a man trying to separate them stumbles backward into Marcus. The impact sends Marcus over the low stone wall, and he falls to his death on the cliffs below. People immediately shout that Richard pushed Marcus. As this happens, Helen sees the flashing lights of police boats arriving at the island.

In the chaotic aftermath of Marcus’s death, the police detain Richard. Guests comfort Naomi, who tried to jump off the cliff after Marcus. Helen gives a statement, omitting her role in orchestrating the confrontation. While other guests avoid her, Renata is the only one who offers comfort.

The police inform Helen that Richard will be held without bail and will likely die in prison in Italy. They also tell her they are treating Marcus as responsible for Lorna’s death, based on the photograph, Naomi’s statement, the money, and the secrets. Helen tells the officer Marcus and Lorna were not having an affair, but he does not believe her. Ciro arrives and takes Naomi and Helen back to the villa.

The next morning, Bud, reports that Richard intends to plead guilty. While Richard has left his personal effects to Helen, all significant assets, including the family home, belong to Naomi. That evening, Freddy takes Helen to dinner and proposes, but she refuses him.

Returning to the villa, Helen finds Naomi drinking heavily. Naomi admits she was the one who killed Sarah after Marcus hesitated. She also reveals she found Lorna’s pregnancy test in Lorna’s room and issued Marcus an ultimatum to handle Lorna or she would stop financing the Lingate family. Naomi blames Helen for Marcus’ death and vows to write Helen out of her will. Seizing the opportunity while making Naomi a drink, Helen crushes the pills she hid from Naomi earlier into a glass of vodka. Naomi drinks it, speaks briefly about Sarah, loses consciousness, and dies.

Naomi’s death is officially ruled a death by suicide. Bud informs Helen that she is the sole beneficiary of Naomi’s estate, making her incredibly wealthy. Helen tells Bud to sell the family’s properties in Los Angeles, and she plans to start a new life in Milan with Ciro.

As Helen prepares to leave the villa, Renata admits that she was the person who sent the snake necklace to Marcus. She implies that the accepted story of what happened 30 years ago is a lie.

Returning late to the villa to retrieve a leftover bag of pastries for Ciro, she discovers Sarah injured but alive in the garden. Sarah manages to whisper that Marcus, Richard, and Naomi are all responsible for her injuries. Renata directs Sarah toward the safety of her cottage. Before following, Renata finds Sarah’s wedding rings on the ground and puts them on her own finger for safekeeping.

As she turns to leave, Naomi attacks her from behind. In the darkness, Naomi mistakes Renata for Sarah, seeing only the red dress and blond hair, and shoves her over the cliff’s edge. Just before she falls, Renata sees the silhouette of Marcus watching from a window in the villa.

Sarah explains that she has been posing as Renata for 30 years. After watching Naomi push the real Renata off the cliff, Sarah escaped to Renata’s cottage, where a discreet doctor treated her head wound. The next morning, Renata’s toddler son, Ciro, accepted her as his mother, and Sarah decided to raise him, knowing the Lingates would murder her if they knew she had survived.

Marcus identified Renata, who was wearing Sarah’s rings, as Sarah to the police, officially declaring Sarah dead. For decades, Sarah maintained her disguise as Renata. During the Lingates’ annual visits to Capri, a hired housekeeper would bring a Helen to her for a week of babysitting, allowing Sarah to secretly remain in her daughter’s life. Pained to see a teenage Helen becoming controlled and unhappy, Sarah decided to act. She dug up the necklace, which she kept buried in her yard, and mailed it to Marcus to force a confrontation that would ultimately free Helen.

Helen lives happily in Milan with Ciro and their infant son, Aaron. Sarah lives nearby and has become a mentor to young artists. Helen sees Lorna in town, follows her around, but loses her. Ciro assures Helen that Lorna is dead, but Helen is unsure.

A woman introducing herself as Silvia confronts Helen in an art supply store. She claims Helen mistook her for someone else and hopes she finds her friend. A week later, Helen is certain she sees the real Lorna across a busy street. They lock eyes for a moment before a tram passes between them. When it is gone, Lorna has vanished, leaving Helen to question what she saw.

Lorna reveals that she is alive and wealthy, having faked her own death. Knowing Helen lacked the capacity to truly escape her family, Lorna devised her own plan. The night she was supposed to leave Capri, she met Martina, one of the girls from Stan’s party, at the marina. Lorna originally planned to stage a crime scene in Naples, but she realizes Martina looked similar enough to Lorna to be used to fake her death. Lorna lured Martina onto Stan’s boat, took her to a remote rocky inlet, and pushed her overboard, knowing she could not swim. Before fleeing, Lorna returned the boat to the jetty, then slept outside waiting for a ferry to Naples. Martina’s body was later misidentified as Lorna’s.

After leaving Capri, Lorna deposited the blackmail money in Switzerland and started dating a financial advisor who reminded her of Marcus. Lorna and her boyfriend went to Milan, where Helen noticed her. Lorna hired Silvia to impersonate her and confuse Helen. The final sighting near La Scala was real; Lorna wanted to see Helen one last time before disappearing forever, after which Lorna returns to Switzerland.