One of Us Is Lying recap

Five Bayview High seniors are sent to detention together: overachiever Bronwyn Rojas, popular Addy Prentiss, baseball prospect Cooper Clay, drug dealer Nate Macauley, and Simon Kelleher, who runs a gossip app called About That. Simon suffers a fatal allergic reaction during the hour, and police find that his drink was contaminated and the school's emergency injectors were gone. Each of the other four was the subject of a post Simon had scheduled for the next day, which gives all of them a motive and turns the case into national news. An anonymous account begins publishing the secrets Simon never got to: Bronwyn's cheating on an exam, Addy's infidelity, Nate's dealing, Cooper's relationship with a young man named Kris. Nate is arrested and charged. Investigating on their own with help from Bronwyn's sister Maeve, the four establish that Simon staged his own death to frame them, with help from Addy's boyfriend Jake and the knowledge of Simon's friend Janae. Jake attacks Addy when she confronts him and is arrested; the four are cleared and left to rebuild.

Five Bayview High seniors are sent to detention by a teacher who finds phones in his classroom that none of them admits to owning: Bronwyn Rojas, an academic overachiever bound for Yale; Addy Prentiss, defined by her long relationship with Jake Riordan; Nate Macauley, on probation for dealing drugs; Cooper Clay, a baseball prospect watched by professional scouts; and Simon Kelleher, who runs About That, a gossip app that trades in other students' secrets. During the hour Simon drinks a cup of water, goes into anaphylactic shock and collapses. He has a severe peanut allergy, no emergency injectors can be found in the nurse's office, and he dies at the hospital. Police establish that the drink was deliberately contaminated, which makes the four students who shared that room the only people who could have done it.

Investigators find that Simon had a post ready for About That naming all four of the other students in detention, and that each of them has something worth protecting: Bronwyn's academic record, Addy's relationship, Nate's probation, and something Cooper has never told anyone. Every one of them therefore has a motive, and the detectives treat them accordingly. The story escapes Bayview and the four become national tabloid material as the Bayview Four, followed by reporters, argued over online, and increasingly isolated at school. Their friends and families take sides, and the school's sympathy runs out quickly. Nate, with a record and the least credibility of the four, draws the most attention from police, while Bronwyn is stunned to be treated as a suspect at all. Thrown together by the investigation, Bronwyn and Nate begin talking to each other properly for the first time.

An anonymous online account starts publishing the material Simon had collected, releasing it one target at a time and keeping the story alive long after it would otherwise have faded. Bronwyn's secret goes first: she stole a chemistry exam in her junior year. The admission costs her the clean record she has built everything on and forces a painful reckoning with her parents and with her own idea of herself. Police read the leaks as evidence rather than as harassment, and the pressure on all four increases. Maeve, better at online research than anyone officially working the case, begins digging into Simon's accounts and the history of the app. Bronwyn and Nate grow closer despite what their families and the town make of it, and Addy's place in her own social group starts to slip.

The anonymous account turns on Addy, revealing that she was unfaithful to Jake with TJ Forrester while Jake was away with his family. Jake ends the relationship in public, her friends drop her, and her mother is no use at all. Addy moves in with her older sister Ashton, cuts off her hair, and begins working out who she is without a boyfriend to organize herself around. Nate is squeezed harder by the detectives and by his probation officer, and his absent mother reappears in his life. Simon's closest friend Janae will not speak to any of the four and becomes harder to reach. Realizing that nobody else is trying to prove them innocent, the four start comparing what they know with each other rather than through their lawyers.

Cooper is outed by the anonymous account: he has been in a relationship with a college student named Kris, hidden from his family and from the scouts courting him. His father takes it badly, Keely learns the truth at the same time as everyone else, and Cooper's future in baseball is suddenly uncertain, though his grandmother stands by him without hesitation. Police then arrest Nate and charge him with Simon's murder, in part because he is the easiest of the four for a jury to believe in. He is held while Eli Kleinfelter of the nonprofit Until Proven takes his defence, and Bronwyn refuses to accept the case against him. With one of them in custody and the others watching it happen, the remaining three start investigating in earnest.

Working with Maeve, the group traces Simon's activity beyond About That and finds that he had been immersed in extreme online forums, reading about people who had made themselves permanently notorious and planning something much larger than a gossip post. The picture that emerges is of a boy who had already decided how his story would end, and who arranged the detention himself: the planted phones, the missing injectors and the contaminated cup were all part of a scheme in which he was the only person in the room who knew what was going to happen. That accounts for the mechanics but not for the help such a plan would have needed, or for who has been running the anonymous account in the months since. Janae, the one person close enough to Simon to know, is visibly falling apart.

Simon staged his own death to frame the four classmates he blamed for his obscurity and to be remembered for it. Jake Riordan helped him: he planted the phones that created the detention and removed the emergency injectors, and he did it as revenge on Addy for cheating on him. Janae, Simon's confidante, was left to keep the anonymous account running afterwards, and finally tells Addy the truth. When Addy confronts Jake he attacks her and nearly kills her before Janae intervenes and Addy escapes; Jake is arrested and charged. The case against Nate collapses and the four are publicly cleared. Cooper is open about his relationship with Kris and keeps his prospects in baseball; Addy has a life of her own and a real relationship with Ashton; Bronwyn and Nate stay together as she leaves for Yale. The four end the year knowing exactly what was done to them and that the person who did it is beyond any consequence.

Simon was never murdered. He staged his own death, planning an elaborate suicide that would look like a killing and would destroy the four classmates he blamed for his standing at Bayview, and he wanted the notoriety that a case like it would bring him. Jake Riordan helped him build it, planting the phones that created the detention and removing the emergency injectors, and did it as revenge on Addy for being unfaithful to him. Janae Matthews, Simon's confidante, was left with instructions to keep the anonymous account posting after his death; she eventually breaks and tells Addy the truth. When Addy confronts Jake he attacks her and comes close to killing her before Janae intervenes and Addy gets away, and Jake is arrested. The charges against Nate are dropped and all four are publicly cleared. Cooper is open about Kris and his baseball prospects survive being outed. Addy, no longer built around Jake, has a life of her own and a real relationship with her sister Ashton. Bronwyn and Nate stay together as she leaves for Yale. The four remain tied to one another by a year that Bayview will not forget, and by the fact that the person who did this to them can never be held to account for it.