A teenaged Hispanic boy has just been tried for the murder of his father, and the case is now in the hands of the jury.. A guilty verdict will send the boy to the electric chair.

The case looks, on the surface, cut and dried, but one juror (Henry Fonda), despite his own feeling that the defendant is probably guilty, feels that the facts, at very least, merit a cursory review, before the jury hands in a guilty verdict. His insistence on a brief examination of the case seems to rub many on the jury the wrong way, as they continue to see the matter as open and shut.

Fascinatingly, in examination of the testimony and facts of the case, the experiences, personalities, attributes, limitations, and biases of the individual jurors weave in and out of the deliberation process, at times to its benefit and at times to its detriment.

To the benefit of the deliberation process, 1) the very elderly juror (Joseph Sweeney) is the only one that can see a possible motive explaining why an elderly witness may have misled the court in his tetimony, 2) the one fellow (Jack Klugman) who grew up in a rough neighborhood, where he witnessed numerous knife fights, is the only one who sees a problem in assuming that the defendant made the stab wound found, and 3) the juror who had done contract work by the elevated subway (Ed Binns) was the only one in a position to question what one of the witnesses might or might not have heard.

To the detriment of the deliberation process, 1) one juror (Ed Begley) is so consumed by his personal prejudices that he sees value in ridding the streets of the Hispanic defendant whether or not he is guilty, and 2) another juror (Lee J. Cobb) is unopen to reason because he has been physically harmed by his teenaged son, and, consequently, views each and every teenaged boy, including the defendant, as capable of patricide.

The number of obstacles on the path to honest assessment of the facts is a constant threat to the deliberation process. Will this jury come together to find a verdict of either "guilty" or "not guilty" or will it be a hung jury (a jury that cannot reach a unanimous decision, and must retire from the case without declaring a verdict)? Watching how this matter is resolved is a riveting study in the nature, and utimate beauty, of the trial by jury process.