A psychotic man opens fire in a diner, murdering numerous people before killing himself. The survivors struggle in different ways following this horrendous event: a doctor doubts his own instincts and elects to use an experimental medical procedure on his wife, while a gambler believes he's on a lucky streak. A waitress begins engaging in promiscuous sex, and a young girl whose father is among the dead gains unexpected fame.
The movie takes place in the three days leading up to Lennon's murder and is intended to be an exploration of Chapman's psyche, without putting substantial emphasis on the murder. The title "Chapter 27" suggests a continuation of J.D. Salinger's novel The Catcher in the Rye, which has 26 chapters, and which Chapman was carrying when he shot Lennon. Chapman was obsessed with the book, to the point