"Charlie" is the alias of the adolescent narrator of the novel, who is about to begin his first year of high school. The novel is presented through letters that Charlie writes to an anonymous person about whom he has heard the girls at school talk fondly. Charlie begins his freshman year apprehensive as a result of the death of his only good friend Michael. Michael committed suicide several months before while they were still in middle school. He does not feel that he can lean on his parents or older siblings for support, because they never truly understood him. He also explains that the only relative that he ever felt close to was his Aunt Helen, but she was killed in a car accident on his seventh birthday.
Charlie soon befriends two seniors, Sam and her step-brother Patrick. He soon develops strong feelings for Sam, but believes that he has no chance being with her. The two introduce him to many new experiences and a group of upperclassmen friends. Charlie writes about situations he gets into with his new friends including going to parties, driving through his town's tunnel and feeling "infinite," seeing and performing in Rocky Horror Picture Show, going on his first date, and trying various drugs. After one party where Charlie took LSD, the police find him passed out lying in the snow somewhere. In the hospital talking to the police and his parents, it is shown that Charlie often has visions, showing that he is not mentally well.
Charlie's English teacher, Bill, also plays a significant role in his life. After giving him a 'B' grade on his book report essay, Bill begins giving him books to read outside of class and encourages him to write essays. He then critiques them to help Charlie develop better diction and syntax, which is reflected in his letter writing. Despite his feelings for Sam, Charlie briefly dates Mary Elizabeth, another girl in their clique. She takes him to their school's Sadie Hawkins and then they go on a couple