One of Us Is Lying by Karen M. McManus

ay close attention and you might solve this.
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.