Simon is not a popular guy in high school. In fact, many of his classmates hold a grudge against the teen because he is the creator of the school's gossip app, which reveals everyone's dark secrets. But only four people were with Simon at the time of his death: Bronwyn, the "Brain"; Cooper, the "Jock"; Abby, the "Princess"; and Nate, the "Rebel."

Yes, it's very The Breakfast Club-esque.

So, is one of them guilty?

In the book, bad boy Nate is jailed after being named the primary suspect in Simon's murder. However, the case is not as simple as it seems.

The four members of the "murder club" become suspicious of Simon's only friend, Janae, who's been absent from school. Addy and Cooper decide to drive to her house and ask Janae some questions. Noticeably on edge, Janae eventually admits that Simon planned his own death.

It turns out that Simon — who had been struggling with depression – died by suicide, but first, wanted to get revenge on some of his peers. Simon was upset that Bronwyn had cheated her way into becoming valedictorian. He didn't like Cooper after the high school jock told Vanessa to not invite him to any parties. And as for Nate, he ruined Simon's chances to be with Keely.

So, what about Addy?

Simon reveals to Addy's boyfriend, Jake, that she has been having an affair with TJ. As a result, Jake decides to help Simon enact his revenge plan against Addy. Following Simon's death, Jake wants Janae to frame Addy for his "murder," but she instead plants the epi-pen in Nate's locker.