Adapted from Reginald Rose's television play, this film marked the directing debut of Sidney Lumet. At the end of a murder trial in New York City, the twelve jurors retire to consider the verdict. The man in the dock is a young Puerto Rican accused of killing his father, and eleven of the twelve jurors do not hesitate in finding him guilty. However, one of the jurors (Henry Fonda), reluctant to send the youngster to his death without any debate, returns a vote of not guilty. From this single event, the jurors begin to re-evaluate the case, as they look at the murder - and themselves - in a fresh light.

Chicago subway worker Lucy (Sandra Bullock) is infatuated by businessman Peter (Peterg Gallagher), a commuter who regularly uses her station and who she only ever sees from a distance. One day, Peter is almost hit by a train, but Lucy manages to save him at the last moment; then, as she sits by his side while he lies unconscious in a hospital bed, his family arrive and mistake her for his new girlfriend. Happy to be welcomed into the home of her dream partner, Lucy tries to gather the strength to set the record straight, but the situation only becomes more complicated when she starts falling in love with Peter's brother Jack (Bill Pullman).