The trial of a teenage Ambiguously Brown boy charged with murdering his father comes to an end, and the judge sends the jury to do their duty and decide on a verdict, reminding them that they should only vote guilty if they have no reasonable doubt about it, and the vote must be unanimous either way.
The initial vote is nearly unanimously guilty, with only Juror 8 voting not guilty, saying he’s not actually sure the defendant is innocent, but feels such a momentous decision shouldn’t be made so easily. The other jurors argue their points and three emerge as the strongest proponents for a guilty verdict: 3 is estranged from his son and has a simmering distrust for all the current young generation, 4 believes in the seemingly ironclad evidence against the defendant, and 10 is simply a racist. Other personalities also become clear: 5 comes from a similar background as the defendant and takes offense to the insults toward “them,” 7 has tickets to a baseball game and just wants things wrapped up quickly, 11 is a European immigrant watchmaker who fled oppression precisely because of things like America’s fair trial system, and 12 is an airheaded ad executive.
The jurors go over the overwhelming evidence against the defendant: he was physically abused by his father all his life, and hours before the murder, neighbors heard him shouting “I’m going to kill you.” He then claims he spent the evening at the movies, but couldn’t remember which ones, and also bought a highly distinctive switchblade knife which was used to kill his father. There are also two witnesses, an old man in a downstairs apartment who heard the murder and then saw the defendant fleeing the scene, and a woman across the train tracks who actually saw the crime through a passing train.
8 asks for the knife to be brought in, and lets everyone talk up just how unmistakable it is before revealing he bought an identical knife from a pawn shop near the apartment building. The others are momentarily shocked, but quickly fall back on how this doesn’t actually prove anything, so 8 takes a desperate gamble, offering to change his vote to guilty if an anonymous ballot reveals everyone else is still voting guilty; should at least one ballot say "not guilty", they will stay and discuss the case. It pays off when the elderly 9 changes his vote to not guilty, simply respecting 8 for standing up for his beliefs alone for so long.
Following a break, the jury starts with a discussion of the two witnesses, and 8 realizes the two testimonies don’t make sense together: the old man wouldn’t have been able to hear anything at the same time a train was going by as the woman said. 9 speaks from his own experience and suggests the old man may have convinced himself he heard it out of a desperate need to be important just once after a lifetime of being ignored. 8 also brings up how “I’m going to kill you” is a common phrase that people hardly ever seriously mean, which is enough for 5 to change his vote to not guilty.
11 questions why the defendant would return to the apartment where he was caught, supposedly to retrieve the knife he left in the corpse. No fingerprints were found on it, making it odd that he’d think to wipe them off but not take the knife with him in the moment. 3 and 10 badger him about supposedly working against "their side", and when another vote is called, 11 changes to not guilty.
The discussion of the old man continues, as he was severely infirm (read: a stroke hampering his ability to walk) yet claimed to have gotten from his bed to the stair door in just fifteen seconds to see the defendant running down them. 8 uses a diagram of the apartment to recreate the distance and approximates his gait, and ends up taking more than twice as long even as some of the jurors say he was a bit fast. By now 3 loses his temper and shouts about how badly he wants the defendant to die, and when 8 calls him a sadist he retorts “I’ll kill him!” when the others hold him back, to which 8 says he’s just proved the point about that phrase.
Another vote is called, and 2 and 6 change to not guilty, making it tied with six on each side. 8 brings up the defendant’s alibi, saying that with the emotional stress the boy was under he could easily have forgotten the movies he saw. When 4 doubts it, he’s challenged to recall a pair of movies he saw several days ago, and he can easily remember the A-picture but not the B-picture, despite not having any stress.
2 brings up the knife again, and how the defendant’s father was killed with a downward stab wound despite being a good deal taller than his son. 3 demonstrates how it’s possible with a Reverse Grip, but 5 uses his experience with seeing knife fights to show how no one experienced in them would use that grip; switching to that would waste too much time. 7 suddenly changes his vote, saying he’s just “had enough,” but after a stern lecture from 11 about the importance of the legal process, he says he actually does believe it.
In another vote, 1 and 12 change to not guilty, leaving only the three strongest holdouts. 10 immediately launches into a tirade against the defendant’s “kind,” putting his racism on full display and causing all the others to turn away from him in disgust one by one. He finally sputters out on seeing no one’s listening, and 4 bluntly tells him to not talk again.
4 takes over the argument by bringing up how they still haven’t addressed the most damning piece of evidence, the woman who actually saw the murder. His argument is so persuasive that 12 changes his vote back to guilty, and 8 is at a loss for how to counter it. But 9 notices 4 rubbing his nose after taking his glasses off, and realizes the woman also did it in court, along with having the marks on her nose that can only be made by regularly wearing glasses. 4 concedes that no one wears glasses to bed, raising enough question about how much she could have seen that he and 10 both change to not guilty, plus 12 changing back.
Now finding himself the one stuck alone, 3 continues to rant about how none of what’s been said proves anything, and moves on to his anger at youth in general before ripping up a picture of his son. It finally dawns on him how much he’s being controlled by his own prejudice, and he sobs out his vote for not guilty, achieving a unanimous vote. As the jurors leave to present the verdict, 8 gives a gesture of reconciliation by helping 3 put his coat back on.
Outside the courthouse, 8 and 9 exchange their names for the first time, Davis and McCardle, before parting with a simple “Well, so long.”
