At the end of a murder trial in New York City, the jurors retire to consider their verdict.
The man in the dock is a young Puerto Rican accused of killing his father, and eleven of the 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.