Eric“Mobe” Calhoune’s best friend Sarah Byrnes is catatonic, sitting in the mental ward of Sacred Heart Hospital. The staff there suggests that he recall some moments that may jog her memory and bring her and back to reality. Eric and Sarah Byrnes (who insists on being called Sarah Byrnes, ratherthan just Sarah) have been friends for a long time, originally because he was extremely overweight and she was severely burned as a child, leaving her with scars on her hands and face. They were picked on regularly and began to write an underground newspaper called Crispy Pork Rinds , focusing an article on the bully Dale Thornton. After the ensuing events, they recruited Dale as“protection”, and their lives became a bit easier.
Eric is recruited to the swim team, and as he improves in skill his weight decreases. Out of fear of losing his friend Sarah Byrnes, he continues to eat, and even tries to eat as much as he can so that he can“stay fat for Sarah Byrnes”, so that he won't stop being an 'outcast' with her and lose her friendship. Eric’s search for a “cure” for Sarah Byrnes’ catatonia leads him to seek out Dale Thornton, and Eric learns that she had an abusive father and that the facial scarring was no accident.
Shortly after being confronted with this information, Sarah Byrnes begins speaking to Eric, and he discovers that her catatonia has been a ruse, and that she is terrified that her father, whose abuse has been worsening, is going to kill her. She has been hiding out in the hospital because it is the only place she feels safe from him. But Virgil Byrnes appears to be on to Sarah's plan, and time is running out. Confused as to what to do, Eric reveals all to his teacher and swim coach, Ms. Lemry. She hatches a plan to hide Sarah Byrnes in the apartment above her garage.
Ms. Lemry teaches the Contemporary American Thought class, which includes discussions on abortion, suicide, religion, body image, social justice, and many other topics. Eric and his atheist friend Steve Ellerby conflict with Mark Brittain, a devout Christian. Mark's girlfriend, Jody Mueller (also Eric's crush), secretly doesn't agree with all of his views. It is revealled that Mark encouraged her to abort his baby. Jody breaks up with Mark and starts going out with Eric. Meanwhile, during the course of this class, Mark is confronted with the truth of his actions. He has difficulty reconciling his actions with his beliefs and later attempts suicide, but fails.
Ms. Lemry agrees to take Sarah Byrnes to Reno to look for her mother, who is the only witness to the abuse Sarah has suffered at the hands of her father. While they are gone, Virgil Byrnes hunts down Eric after school and threatens to kill him, and eventually stabs him in the back and cheek. Eric makes his way to Dale Thornton’s house, where he passes out, and Dale and his father rescue him and take him to the hospital. Sarah attempts to run away because she doesn’t want any more of her friends to get hurt, but Eric and Ms. Lemry stop her. Eric’s mother’s boyfriend, Carver Middleton (former Vietnam Special Forcessoldier), figures out that Virgil Byrnes must be hiding out in his house and lays a trap for him, capturing him and severely injuring him, which lands Carver in jail.