The Quick Recap and Section-by-Section Summary for One of Us Is Lying by Karen McManus are below. Spoiler warning: these summaries contains spoilers.
For a non-spoiler version of the plot synopsis, see The Bibliofile's review of One of Us Is Lying by Karen McManus.
In Part One, Simon Kelleher, a high school student and loner at Bayview High, dies under suspicious circumstances from allergic reaction in detention. Simon writes a gossip blog, and it's discovered that he was about to post incriminating information about four students in the room (Bronwyn Rojas, Nate Macauley, Cooper Clay and Addy Prentiss). They're also the four other students who were in detention, and they quickly become the prime suspects in Simon's death (known as the Bayview Four).
In Part Two, Simon's unpublished post goes up on an anonymous Tumblr account, revealing its trove of secrets. (Addy cheated on her boyfriend Jake with his best friend, TJ Forester. Cooper, a baseball player, used drugs to improve his fastball. Nate is dealing drugs/painkillers. Bronwyn cheated by stealing tests to get an A in chemistry.) Bronwyn's sister Maeve hacks Simon's blog and starts to research him to get clues.
In Part Three, the four team up to compare notes and sense something is off with a student named Janae, who had been Simon's only friend. They also note that Simon resented them all for various reasons. Soon, however, Nate (the school bad boy) gets arrested for Simon's death since there's indications he runs the anonymous Tumblr account. Finally, Addy confronts Janae, who breaks down and admits the truth that Simon killed himself. He convinced Janae and another guy, Jake (who had once been Simon's childhood friend and Addy's boyfriend who she had cheated on), to help him frame the other four students. Simon was planning on having Janae release a manifesto about it in a year. After a scuffle, Jake and Janae are arrested, though Janae gets a plea bargain.
In the Epilogue (three months later), the four have become good friends despite all being very different types of people. Bronwyn (good girl) and Nate (bad boy) begin dating.
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Part One: Simon Says
Chapters 1 – 4
Bronwyn Rojas, Simon Kelleher, Nate Macauley, Cooper Clay and Addy Prentiss are students at Bayview High. They’ve all be sent to detention for having phones in class, which is not permitted. However, the phones they got in trouble for weren’t theirs (planted by someone else), but Mr. Avery doesn’t believe them.
Simon runs the gossip app (“About That“) for their school (where he posts about other people’s secrets). A lot of people dislike him for it, but it’s never been wrong. Bronwyn is the “good girl”/”brain”. Cooper (“Jock”/homecoming king) and Addy (homecoming princess) are the popular kids. Addy’s boyfriend is Jake. Cooper’s girlfriend is Keely, though he’s cheating on her. Nate is the school troublemaker. Nate’s mother left when he was young and his father is an alcoholic on disability, so he sells drugs (painkillers) for extra cash.
While in detention, there’s an accident in the parking lot, and Mr. Avery leaves to check it out. Simon goes to get a cup of water, takes a sip and has an allergic reaction. The others look for an epi-pen as he chokes, but can’t find one. Abby calls 9-1-1. Cooper runs to the nurse’s office, but the emergency epi-pens aren’t there. The paramedics arrive, but they soon hear Simon has died. The four others are told they each attend one-on-one counseling sessions in the wake of Simon’s death. The autopsy reveals Simon ingested peanut oil somehow.
A few days later, on tumblr, someone has anonymously posted a confession titled “About This” about killing Simon because of his gossip app.
Chapters 5 – 9
The tumblr account soon anonymously posts again, saying that it’s someone who was in detention, and the person admits to taking all the epi-pens from the nurse’s office. The police note that Addy had been in the nurse’s office earlier that day. Addy lies at first and says she wasn’t there. Then, when pressed, Addy says it was to get ibuprofen.
Detectives Wheeler and Chang shows up to question the students. They reveal that Simon’s next post was written, but was never posted before he died. Each of the four were mentioned in that post. Addy once cheated on her boyfriend Jake with his best friend, TJ Forester. Cooper’s fastball has recently improved dramatically (he’s a baseball player), which About This attributes to juicing (perfomance-enhancing drugs). Nate is on probation, but he’s still dealing drugs (painkillers). Bronwyn cheated (stealing tests from the teacher’s computer) to get an A in chemistry.
The police have a theory that they jointly planned the murder, which they all deny. Nate’s probation officer warns him that as the poor kid and the one on probation, he’s the obvious scapegoat, so he needs to tread carefully. He stops dealing drugs. Meanwhile, Addy figures the news about her and TJ will come out anyway, so she admits to Jake that she cheated on him. He dumps her.
Part Two: Hide-And-Seek
Chapters 10 – 18
After Simon’s funeral, Simon’s post with all the secrets appears on the About This tumblr, outing Nate, Addy, Cooper and Bronwyn. The news picks up the story, dubbing them the Bayview Four. Mikhail Powers, a TV reporter, starts reporting on it. Anonymous posts continue to appear on the tumblr, claiming to be from the killer who is one of the Four.
The person most sad about Simon’s death is Janae, Simon’s only real friend. Addy tries to comfort her after Simon’s death. Jake was friends with Simon when they were younger, but not anymore. Most people disliked Simon. Leah Jackson attempted suicide due to Simon’s reporting on her sex life. Another student, Aiden Wu had a breakdown when Simon outed him for cross-dressing.
Cooper and Addy each get lawyers. Now that Addy is not with Jake, she loses most of her friends other than Cooper. TJ also tries to be nice to her. Addy’s sister Ashton tries to help Addy figure out who she is separate from Jake. Addy admits she lied about being in the nurses’s office because the ibuprofen was for Jake, and she didn’t want to reinforce Ashton’s feeling that she let Jake treat her like a doormat.
Meanwhile, Cooper dumps Keely, since he realizes he doesn’t like her that much. Keely tells him about hooking up with Nate before they started dating to try to get a reaction, but Cooper doesn’t care.
Bronwyn’s parents hire Robin Stafford as her defense lawyer. Bronwyn also reaches out to Eli Kleinfelter, a lawyer at a legal defense non-profit called Until Proven, to ask for advice. Bronwyn finds herself but Nate offers her a cheap burner phone so they can communicate. She takes it, and Nate and Bronwyn start chatting. She plays piano for him. Soon, things get romantic.
Bronwyn’s sister Maeve hacks into Simon’s About That app to get some clues, and she starts researching Simon’s other online activities. Maeve had also been targeted by Simon a year before. The police dig up that post, and they question Bronwyn about it. Simon had cruelly mocked Maeve over a crush and made a dismissive remark about her having had cancer. In the comments section, there’s one from Bronwyn telling him to drop dead.
Nate’s long-absent mother shows up at his door. Cooper meets up with the person he was cheating on Keely with which turns out to be a guy named Kris.
Part Three: Truth or Dare
Chapters 18 – 23
Nate has dinner with his mother. She has gotten sober lately and has a stable job.
Maeve locates a bunch of Simon’s prior activity in 4chan threads where he cheers on school shooters and things like that. She forwards those to reporters. She also encourages Leah to talk to reporters about how Simon’s gossip caused her suicide attempt.
Janae asks Addy to hang out and she agrees. Janae tells her that Simon resented being an outsider. They go to Addy’s place. Janae asks for something to drink and then leaves suddenly. Addy then receives a text from Bronwyn warning her to be careful around Janae.
Cooper is in love with Kris, but is afraid to tell his dad. Cooper’s also the only one whose allegations on About That are false. He wasn’t on steroids. However, the police reveal that Cooper’s entry had been altered. Instead, there’s a previous entry that was encrypted which reveals Cooper’s relationship with Kris. They question him about the new revelation, and Cooper has no choice but to come out to his parents. After the police question more students, the secret is out, and at school, the kids tease Cooper. However, Nate, Addy and Bronwyn all stick with him, along with his friend Luis.
The four meet up to discuss the situation and compare notes. Regarding Janae, Bronwyn notes that Janae has been hanging around them a lot, which is unusual. And it seemed like Janae and Simon had a falling out before he died. Janae has been losing weight ever since Simon’s death.
They also note Simon’s resentment. Simon had been interested in Keely, but she had hooked up with Nate and dated Cooper. Plus, Bronwyn and Leah had gotten Simon disqualified from Model U.N. by accidentally giving him a wrong date for a deadline. So, Simon was bitter with Nate, Bronwyn and Cooper, and maybe Addy since she is one of Keely’s best friends.
The four also wonder about the car (red Camaro) that just happened to get in an accident, leading Mr. Avery to leave the room. Cooper asks Luis’s brother, who works at the auto shop, if any cars like that have been in the shop lately.
That night, Mikhail Powers is on again covering the Bayview Four. But this time, the focus is different. Instead of dragging their names through the mud, he’s angry that the police outed Cooper. Mikhail notes that many others had reason to hate Simon. Aiden and Leah are featured, along with Simon’s 4chan activity.
Bronwyn is feeling hopeful, but then she finds out Nate has been arrested for Simon’s murder.
Chapters 25 – 28
Bronwyn contacts Eli and begs him to help Nate. Eli sees that there’s weird stuff going on with the police “discovering” new evidence in places they’d already searched. He eventually agrees and takes on the case, and Bronyn connects him with Nate’s mother, Ellen Macauley. Bronwyn, Addy and Cooper get together to discuss. They look through the tumblr posts, since the police think Nate wrote them. Addy stops at a post that describes the four of them catching a Detective Wheeler eating a donut. It’s something that never happened, but Addy told Jake that it had.
With Luis’s brother’s help, Bronwyn tracks down the red Camaro. The owner is Sam Barron. When prompted, he admits a guy paid him and his friend $1,000 each to get into the fender bender. He says it was Simon.
The four of them meet again, plus Kris and Ashton, Addy’s sister. Kris suggests that Simon killed himself and tried to take them down with him. They realize it makes sense. They then wonder if Jake was his accomplice, since Simon and Jake had once been friends, possibly because Simon had told Jake about Addy’s infidelity.
Chapter 29 – 30
Addy shows up at Janae’s house. Janae looks terrible. Addy comforts her, and Janae finally breaks down and admits that Simon did it to himself. Janae hands over a manifesto that she was supposed to give to police one year later where Simon confesses to his plan. Janae also tells Addy that Simon had rigged the votes for homecoming court to get on it, and Jake found out. So, Simon used the information about Addy and TJ to shut Jake up and to get Jake to help him. Jake was the one writing the tumblr posts. Jake also threatened to frame Janae when she got queasy about it. Jake also changed Cooper’s entry because he didn’t want people to think he was best friend with someone gay.
Finally, Janae says that Jake wanted her to plant a computer (linked to the tumblr posts) in Addy’s room to frame her, but Addy had been nice to her, so she chickened out. She framed Nate instead.
Jake shows up unexpectedly, and Janae and Addy quickly hatch a plan to secretly record him. They want evidence of his involvement to take to the police. Addy hides in the closet and records as Janae and Jake talk. However, her phone chimes and he finds her. She runs and he attacks her until Cooper shows up and stops him.
Jake is arrested. Addy and Janae are injured, but will be fine.
As the dust settles, Cooper plans to give Keely a proper apology for their relationship. He also plans to skip the draft and wants to attend USC, where Kris is a student. Eli has been courting Ashton. Janae is getting a plea bargain in exchange for her testimony.
Nate is freed, but feels like he was useless compared to the rest of the Four. With that weighing on him, plus the rest of his baggage, he feels like Bronwyn is too good for him and unceremoniously breaks up with her.
Epilogue: Three Months Later
Bronwyn is now dating a friend, Evan Neiman, and she’s waiting to hear back from Yale. Nate has been avoiding her.
That night, Bronwyn does a piano solo with the San Diego Symphony. Cooper, Addy, Kris, Ashton and Eli all show up to support her. Then, she finds out Nate was there, and he brings her flowers. He says that Addy has been bugging him about having a proper conversation with Bronwyn.
The book ends with them agreeing to try hanging out again as friends again (with the obvious implication that they both want it to be more than that).