The story begins after closing arguments have been presented, as the judge is instructing the jury. The twelve men must determine, unanimously, whether the accused is innocent or guilty of the charge of murder. These twelve then move to the jury room, where they begin to become acquainted with the personalities of their peers. In a preliminary vote they are startled to find that one juror has voted "not guilty." Many of the jurors are amazed and angry because "Davis" (Jack Lemmon), the lone dissenter, does not see the "open and shut" nature of the case. Davis maintains that he has a reasonable doubt, and it is morally wrong (and illegal) to condemn a man to death if any jury member has a reasonable doubt.
The ensuing arguments and sifting of the evidence unveil the flaws of the prosecution's case, the questionable representation by the defendant's court-appointed attorney, and the true character of each of the jury members. Throughout the deliberations, not a single juror knows another by his name. Gradually, Davis and those jurors who become convinced by the soundness of his reasoning prove to every man on the jury that the defendant's guilt is not "beyond a reasonable doubt". The result is a vote of 12-0 in favor of acquittal, and the jurors leave the room. What happens in the courtroom after that is left to the