The story begins with the arrival of a new student, Mary "Mouse" Bedford (Mischa Barton), who is shy and introverted. She is assigned to share a room with two seniors, Pauline "Paulie" Oster (Jessica Paré) and Victoria "Tori" Moller (Piper Perabo). Paulie and Tori are in a romantic relationship, but they keep it a secret from everyone, including their families.
As the days go by, Mouse becomes close to Paulie, who introduces her to her passion for literature and poetry. However, the relationship between Paulie and Tori starts to fall apart, and Paulie becomes increasingly obsessed with Tori. When Tori decides to end their relationship and start dating a boy, Paulie's mental state deteriorates rapidly.
Paulie's behavior becomes erratic and dangerous, and she starts to alienate everyone around her, including Mouse. Eventually, Paulie's actions lead to tragedy, and the film ends with the aftermath of the event.
Lost and Delirious explores themes of love, friendship, sexuality, and mental health. The film received mixed reviews upon its release but has gained a cult following over the years for its honest portrayal of teenage emotions and the complexities of same-sex relationships.