Plot
David Kim lives in San Jose, California with his daughter, Margot. His wife, Pamela, was diagnosed with lymphoma and died before Margot entered high school.
Margot tells David that she is with a study group and will be there all night. Later that night, Margot attempts to call David three times, but he is asleep. The next day, David is unable to contact Margot. Believing she is at her piano lesson, David calls the instructor, but is told that Margot canceled her lessons six months earlier. David files a missing person report, and the case is assigned to Detective Rosemary Vick. Through her social media accounts, David learns that Margot has become a loner since Pamela's death. He discovers Margot had pocketed the piano lesson money and transferred the $2,500 to a now-deleted Venmo account. Vick reports Margot made a fake ID and shows traffic camera footage of her car outside the city, suggesting she may have run away.
Unconvinced, David discovers Margot had been using a streaming site called YouCast, and befriended a young woman named Hannah. Vick reports Hannah's innocence, having been sighted in Pittsburgh at the time of the disappearance. From Margot's Tumblr account, David discovers she frequently visited Barbosa Lake near the highway where she was last seen. He finds her Pokémon keychain there, and the police discover her car in the lake, which contains an envelope with $2,500. A search party is organized, but a storm delays the operation.
After David has an altercation with a boy who claims to know Margot's whereabouts, Vick tells him he can no longer participate in the investigation. Undeterred, David visits TMZ, which displays the crime scene photographs, and notices his brother Peter's jacket. He discovers text messages between Margot and Peter that suggest an incestuous relationship. Upon confrontation, Peter explains they were only smoking marijuana and confiding in each other. He chastises David for being negligent towards Margot, who is still grieving Pamela's death. Vick calls David and tells him an ex-convict named Randy Cartoff confessed to raping and killing Margot before committing suicide.
An empty-casket funeral is arranged. As David uploads photos to a funeral streaming site, he notices the website's stock photograph features a picture of Hannah. Discovering she is a stock model, he contacts her, and she reveals that she does not know Margot and that the police never called her. David calls Vick to report this, but instead reaches a police dispatcher, who reveals Vick was not assigned to the case but volunteered. He discovers she knew Cartoff through a volunteer program for ex-convicts. Reporting this to the sheriff, David confronts Vick, who is arrested at the funeral.
Vick agrees to confess, in exchange for leniency for her son, Robert. Having a crush on Margot, Robert used the YouCast account as Hannah to get close to her. Margot sent money to Robert's Venmo account, believing he was a working-class girl whose mother had cancer. Ashamed for lying, Robert wanted to confess and return the money in person, so he followed Margot to Barbosa Lake to reveal himself. He surprised her by getting into her car, and she ran, with him accidentally pushing her off a cliff into a 50-foot-deep ravine. Assuming the accident was fatal and could be perceived as manslaughter or even first-degree murder, Vick decided to cover up the incident, pushing the car into the lake and fabricating the fake ID evidence. After David found the car, Vick turned Cartoff into the fall guy and staged his confession.
Vick reveals Margot is still in the ravine, suggesting that even if she had survived the fall, she could not have lived five days without water. David tells the police to return to the ravine, remembering the storm on the third day of the search, which would have provided water. The rescue crew finds Margot severely injured but alive.
Two years later, Margot applies for college to major in piano. David tells her Pamela would have been proud of her. Margot changes her desktop picture from one of Pamela and her to the one David sent her of the two of them after the rescue, reflecting a closer relationship between them.
