Diana Baring is a stage actress who is convicted of the murder of Edna Druce, another actress in her theater troupe. Sir John Menier, another actor (who has apparently been successful enough to be knighted), is a juror at her trial. Menier is the last holdout against her conviction, and remains doubtful about the verdict. He decides to launch his own investigation, which reveals the truth behind the crime.
This was Hitchcock's first whodunnit. At the same time Hitchcock directed this film, he also directed a German-language version, called Mary, using the same sets. That version starred Alfred Abel, who played Joh Fredersen in Metropolis.
This work exhibits the following tropes:
- Ambiguously Gay: According to the script, Fane's motive was a desire to conceal his mixed ancestry. However, as played on the screen, it looks a lot more like Fane was trying to conceal his sexuality. Fane as an actor specializes in female impersonation, and is called a "100% he-woman" by another actor. Actor Esme Percy plays Fane as an effeminate, nearly Camp Gay stereotype. The scene where Fane is questioned by Menier as he's putting on woman's makeup has an effect not unlike The Reveal with Anthony Perkins in Psycho thirty years later.
- Better to Die than Be Killed: After it becomes clear to Fane that Sir John knows he murdered Edna, he decides that if he's going to be hanged publicly, he'd rather do it himself; after one final performance on the trapeze, he wraps a safety rope around his neck and jumps to his death.
- Catch the Conscience: Played straight, and with the appopriate shout-out to Hamlet, as Menier calls the murderer in for an audition and has him rehearse a play based on the Druce case.
- Chekhov's Gunman: Sir John, the lead character, is not revealed until a good 20 minutes have gone by, and when he's first seen he's just one face in a quick montage of the 12 jurors.
- The Coconut Effect: In universe and literally, as one of the actors claps the halves of a cocoanut together to simulate a horse's hooves.
- Coincidental Broadcast: Sir John turns the radio in his bathroom on. Seconds later, the announcer delivers a news report about Diana's impending execution.
- Creator Cameo: Hitchcock made one in all of his films. Here he walks by as Menier and his assistants are leaving Diana Baring's rooming house.
- Half-Breed Discrimination: Fane's motive for murder, as Edna was going to reveal to Diana that Fane was a half-caste. However, this seems like code for a Depraved Homosexual motive (see above).
- Have a Gay Old Time: Menier saying "That's queer" about a strange fact invokes this trope. A little girl saying "He's got my pussy!" as her kitten crawls over Menier invokes this even more painfully.
- I Never Said It Was Poison: Marshall asks Fane, while they are rehearsing the fake play, why Fane assumed the murderer came in through the window.
- Inner Monologue: Menier starts thinking about the case while he's shaving. In 1930, early sound recording technology did not allow for overdubbing—Herbert Marshall's dialogue could not be dubbed over the shot of him staring into the mirror. So Alfred Hitchcock had Marshall record the dialogue elsewhere, and the recording was played on the set as the camera rolled.note This is believed to be the first-ever use of voiceover to convey a character's Inner Monologue. This might be the Trope Maker, as stage plays had the characters talk to the audience to reveal their thoughts.
- Leaning on the Fourth Wall: At the end, Diana embraces Sir John. The camera pulls back to reveal that they are acting in a play. The curtain then falls, ending the play and the movie both.
- Match Cut: A curtain rising for a stage performance is matched with the cover to the observation window in Diana's cell being pulled up.
- Rogue Juror: Downplayed; initially, only seven jurors believe Diana is Edna's murderer, while three - Sir John, Mr Daniels, and Mrs Ward - believe she is innocent, and two - Mr Shackleton and Mr Matthews - aren't sure. However, in short order, the two abstensions are quickly persuaded to vote "guilty", Mrs Ward decides that Diana being in a fugue state doesn't remove the risk that she will kill again, and Mr Daniels is called out for only voting "not guilty" because he thought Diana seemed too nice. Sir John holds out for longer than the other four combined, as he is sure that something about the evidence doesn't add up, but when he is unable to provide a solid explanation for his doubts, his fellow jurors pressure him into voting "guilty".
- Speak in Unison: "Any answer to that, Sir John?", say all the other jurors in unison, as they cite the evidence and browbeat Sir John into changing his vote to Guilty.