The film is set against the background of a young student, Charlie, who according to Wikipedia has been suffering from clinical depression from childhood setbacks and has recently been discharged from a mental health care institution to begin his adaptation to a normal lifestyle as a young high school student. Charlie (Logan Lerman) is uneasy about beginning his freshman year of high school; he is shy and finds difficulty in making friends, but he connects with his English teacher, Mr. Anderson (Paul Rudd).
When he sits with two seniors, Sam (Emma Watson) and her stepbrother Patrick (Ezra Miller), at a football game, they invite him to tag along to several social activities with them. At a party, Charlie unwittingly eats a cannabis brownie, gets high and discloses to Sam that the year before, his best friend committed suicide. He also walks in on Patrick and Brad (Johnny Simmons), a popular athlete, kissing. Sam realizes that Charlie has no other friends so she and Patrick make a special effort to bring Charlie into their group. Sam needs to improve her SAT scores to be accepted to Pennsylvania State University, so Charlie offers to tutor her. On the way home from the party, when the three hear a song with which they are unfamiliar, Sam instructs Patrick to drive through a tunnel so she can stand up in the back of the pickup while the music blasts.
At Christmas, Sam gives Charlie a vintage typewriter to help his aspirations of being a writer. The two discuss relationships, and Charlie reveals he has never been kissed. Sam, though already involved with someone else, tells Charlie she wants his first kiss to be from someone who loves him, and kisses him. Charlie, in love with Sam, begins to try to find ways to show her how he feels.
At a regular Rocky Horror Picture Show performance, Charlie is asked to fill in for Sam’s boyfriend Craig, who is unavailable. Their friend Mary Elizabeth (Mae Whitman) is impressed and asks Charlie to the Sadie Hawkins dance. Charlie goes along with the resulting relationship to avoid hurting Mary Elizabeth’s feelings, but grows more and more irritated by the situation. Finally, at a party, when Charlie is dared to kiss the most beautiful girl in the room, he chooses Sam, upsetting both her and Mary Elizabeth. Patrick recommends Charlie stay away from the group for a while, and the isolation causes him to sink back into depression. He experiences flashbacks of his Aunt Helen (Melanie Lynskey), who died in a car accident when he was seven years old.
When Brad shows up at school with a black eye having been caught by his father having sex with Patrick, he lies, saying that he was jumped and beaten up. Brad distances himself from Patrick, calling him a “faggot”. Brad’s friends begin beating Patrick, but Charlie forcefully intervenes, then blacks out. He recovers to find he has bruised knuckles and Brad’s friends are on the floor, incapacitated. Charlie threatens, “Touch my friends again, and I’ll blind you,” then leaves. Sam and Patrick express their gratitude to Charlie, and the three become friends again.
Sam is accepted into Penn State, and breaks up with Craig on prom night after learning he has been cheating on her. The night before she departs, she brings Charlie to her room and asks him “Why do I and everyone I love pick people who treat us like we’re nothing?” to which he repeats advice he received from Mr. Anderson, “We accept the love we think we deserve.” They confide in each other and kiss, but when Sam touches Charlie’s thigh, he experiences a momentary flashback of his Aunt Helen, which he passes off as nothing, and they continue to kiss. After she leaves for college, though, his emotional state deteriorates and his flashbacks worsen. He calls his sister blaming himself for Helen’s death, and admits he may have wished it upon her. His sister realizes he is in trouble and calls the police. Charlie passes out as they burst through the door and wakes up in a hospital, where psychiatrist Dr. Burton (Joan Cusack) manages to bring out Charlie’s repressed memories of his aunt sexually abusing him.
Charlie then is later visited by Sam and Patrick. Sam explains what college life is like, and how she has found “The Tunnel Song” — “Heroes” by David Bowie. The three revisit the tunnel, where Charlie kisses Sam again and stands up in the back of the truck. Charlie acknowledges that he feels alive and in that moment—”We are infinite.”
