Sixteen-year-old Sydney Ellison does her best to act normal, to keep the obsessive thoughts at bay, but she has obsessive compulsive disorder, and so she is constantly surrounded by a stream of dark thoughts she fears she has no control over. After she discovers a body in the woods with her best friend Fran, Syd can't turn off the thoughts, but Fran is the one that wants to investigate. All the while, Syd is trying to manage a budding romantic relationship with a boy she's always admired. Syd feels that her brain is consistently getting worse, not better, and though she's trying to help herself get better, she doesn't trust herself.