Aza, a 16-year-old high school student, is the protagonist of the novel. Aza suffers from obsessive-compulsive disorder, with an extreme degree of anxiety and hypochondria. Her fear of bacterial infection is paralyzing and consumes her mind on a regular basis. Her obsessive thoughts and compulsive behavior interfere with her daily life and with her maintenance of interpersonal relationships. She has known her best friend Daisy since childhood, but Aza’s mental illness prevents her from giving Daisy reciprocal support and attention. Aza begins a romantic relationship with Davis but must break it off because her anxiety will not allow physical intimacy. Aza’s mental health deteriorates throughout the story, to the point that she feels compelled to swallow hand sanitizer to momentarily quiet the insistent terror of bacteria.

When Aza and Daisy embark on a mission to collect a reward for information on the disappearance of Russell Pickett, Aza is reunited with the man’s son, Davis. Aza had previously been friends with Davis when they met at a camp for children who had lost a parent, but she has not seen him in many years. Davis and Aza feel that they are kindred spirits who understand each other’s loneliness and pain.