Act I

The program opens as a judge instructs the jury in a murder case that their verdict must be unanimous. In the jury room, an initial vote is 11 to 1 in favor of guilty. Juror #8 (Robert Cummings) is the holdout voting not guilty. Juror #3 (Franchot Tone) criticizes Juror #8 as being "out in left field." They go once around the table, each juror having an opportunity to express his point of view. Juror #10 (Edward Arnold) focuses on the neighbor who testified that she saw the defendant stab his father. Juror #7 (Paul Hartman) focuses on the defendant's record – reform school at age 15 for stealing a car, arrested for knife fighting, and he comes from slums that are breeding grounds for criminals. Juror #5 (Lee Phillips) takes offense and points out that he's lived in a slum his whole life – "maybe it still smells on me."

Juror #8 asks for the alleged murder weapon, a switchblade, to be brought into the jury room. Juror #4 points out that the shopkeeper where the defendant purchased the knife testified that it was the only one he had in stock and that it is a very strange knife. When the knife is brought into the jury room, Juror #8 pulls an identical knife from his pocket, and reveals he bought one from a junk shop around the corner from the defendant's house, suggesting it is less "strange" than what the shopkeeper thought.

Juror #8 asks for a secret ballot. If there are still 11 guilty votes, Juror #8 will go along. The votes are handed in.

Act II

There are now only 10 guilty votes. Juror #9 (Joseph Sweeney) admits that he was the one who changed his vote.

Juror #8 focuses on the noise from the elevated train that passed by as the murder took place. One of the witnesses, an old man, claimed that he heard the defendant say, "I'm going to kill you," and then heard the body drop one second later. He questions how the witness could have heard these things, at a distance, with the train roaring by. Juror #5 changes his vote to not guilty. The vote is now 9–3.

Juror #8 next questions how the old man who's had a stroke and walks with two canes could have gotten up out of bed and run through his apartment to see the defendant running down the stairs. The old man testified this happened only 15 seconds after the murder. Juror #3 notes the old man was confused during the trial and suggests he may not have been precise when he stated it was 15 seconds. Juror #3 and the others pause, reacting to the import of Juror #3's question. Juror #8 performs a reenactment to show that the old man could not have gotten up and walked that distance in 15 seconds. Juror #3 complains about Juror #8's dishonesty and insists the defendant must face punishment. When Juror #8 calls Juror #3 a sadist, Juror #3 lunges and threatens to kill him.

Act III

A new vote is taken. It is now 6–6. Juror #2 (John Beal) is troubled by the angle of the stab wound. Juror #5 has experience with switch blades and says they are typically used with an underhand motion, but the wound here was from an overhand motion. Another vote is taken, and it's 9–3 in favor of acquittal. Jurors 3, 4 and 10 are now the holdouts.

Juror #10 focuses on race, insisting the defendant must be guilty because, among other assumptions, "There isn't one of them that's got any good in them." The other jurors react in shock at Juror #10's tirade, and Juror #4 threatens Juror #10 to not speak again for the rest of the deliberation.

Juror #4 is still persuaded by the old lady who said she saw the defendant stab his father. One of the jurors recalls that the old lady wore glasses. She wouldn't have been wearing her glasses in bed, which is where she said she was, tossing and turning. Juror #8 says that all the old lady could have seen, without her glasses and through the train windows, was a blur. Juror #3 is left as the only guilty vote, but he finally gives in. The defendant is found not guilty.