One of Us Is Lying by Karen M. McManus
On Monday afternoon, five students at Bayview High walk into detention. Bronwyn, the brain, is Yale-bound and never breaks a rule. Addy, the beauty, is the picture-perfect homecoming princess. Nate, the criminal, is already on probation for dealing. Cooper, the athlete, is the all-star baseball pitcher. And Simon, the outcast, is the creator of Bayview High's notorious gossip app. Only, Simon never makes it out of that classroom. Before the end of detention Simon's dead. And according to investigators, his death wasn't an accident.