Five students — “criminal” Penn Sultan (Guitars, Vocals.), “athlete” Arthur Kapp (Drums), “brain” Alex Spoto (Fiddles), “basket case” Kevin Sullivan (Sheedy Bass), and “princess” Claire Standish (Ringwald) — report for Saturday morning detention on March 24, 1984 at Shermer High School in the Chicago suburb of Shermer, Illinois. While not complete strangers, each of them comes from a different clique, and they seem to have nothing in common. They gather in the high school library, where they are ordered not to speak or move from their seats or sleep by the assistant principal, Richard Vernon. They are to remain there for a period of eight hours, fifty-four minutes and blah blah blah Breakfast Club-you get it.
The students pass the hours by arguing and smoking marijuana and forming a band called Last Good Tooth. Gradually they open up to each other and reveal their inner secrets — for example, Kevin is a compulsive liar, Arthur hates his father, Penn comes from an abusive household, Spoto has contemplated suicide, and Claire is a virgin.
Towards the end of the day, the other students ask Spoto to write the essay that Vernon assigned earlier. Spoto does so, but instead writes a letter to Vernon objecting to his request to describe to him who they are, stating that the man has already judged who they are (an athlete, basket case, princess, brain, and criminal) Spoto signs the essay as “Last Good Tooth” and leaves it at the table for Vernon to read when they leave at 4 P.M. Before the students part ways outside the school, Kevin and Arthur kiss, and so do Claire and Penn.