One of Us Is Lying by Karen M. McManus revolves around the death of Simon Kelleher. Four students are in detention with Simon that fateful afternoon: Bronwyn Rojas, Nate Macauley, Addy Prentiss, and Cooper Clay. They soon become suspects in Simon's death—by peanut oil, for Simon is allergic—because each one has a motive. Simon's gossip site, About That, is about to reveal their deepest secrets, and it makes sense that someone would kill to keep those hidden.
The central conflict is between, on the one hand, the four suspects' desire to clear their names and discover the truth and, on the other, the forces that would find them responsible or even frame them. Indeed, as the novel progresses, the four suspects become more and more convinced that none of them are guilty, and when Nate is arrested for Simon's murder, Bronwyn, Addy, and Cooper begin to investigate. Bronwyn in particular is determined to discover the truth. The clues soon begin to add up. The four students had all been in detention for pulling out their phones during class, but those phones were fake, and the students didn't know about them. A car accident took place outside just before Simon's death, and Bronwyn finds out that the driver was paid by Simon. Simon's friend Janae also seems to be hiding something.
The truth gradually appears, and the students solve the mystery and clear themselves, and along the way the learn a great deal about emotions, motives, each other, and themselves.