This movie grabbed my attention mostly for the involvement of James Whale. He is known best for directing Frankenstein, Bride of Frankenstein, The Old Dark House and The Invisible Man. The Kiss Before the Mirror was a movie he directed between the latter two films, and later remade as Wives Under Suspicion. This is the second non-horror movie directed by Whale I've seen. The first was Waterloo Bridge, featuring a young Bette Davis and pre-Frankenstein Mae Clark.
Being single has its points – at least no-one will ever murder me.
Walter finds his wife undressing in her paramour's bedroom and shoots her dead through the window. He immediately calls the police and gives himself up.
He recounts the events to his best friend, Paul, who is also the attorney defending him. The 'kiss before the mirror' was the one he gave her when he showed up unexpectedly, as she was getting dolled up to meet her lover. She got irritated because his sloppy kiss messed her hairdress, and he was not feeling the love. He followed her and discovered her infidelity, but was so traumatized, he couldn't recall how he did the deed to his lawyer.
When the attorney goes home and sees his wife, Maria, exhibit the exact same behaviors before the mirror, he gets suspicious. He decides to test the theory by grabbing her and forcing a brutish kiss on her, and when she reacts with displeasure, he suspects her.
She goes to meet her lover and attempts to call off the relationship, as the murder of her unfaithful friend has got her unnerved, but he convinces her to say goodbye up in his apartment. Paul has been hiding in the bushes and discovers the truth, allowing him to understand how his friend killed his wife. His plan is to use his understanding to get his buddy acquitted, setting a precedent to get him likewise absolved when he kills his own wife.
At the trial, after an impassioned argument, Paul pulls a revolver from his pocket and points it at his wife, causing her to scream and faint. He then argues that any guy could go nuts just by thinking of being betrayed by a woman. His stunt is successful and the jury finds Walter not guilty.
Paul confronts his wife and uses the revolver in the end.
Paul: He was stunned by her betrayal of him. Momentary insanity induced by jealousy. On that defense, would you acquit him?
Hilda: I don't know. As a woman, I would instinctively find him guilty. One shouldn't encourage men to commit murder, although, it's a great compliment to us when, under the circumstances, men might even murder us.
Paul: What was she doing?
Walter: The most important thing in a woman's life–she was admiring herself.
Maria: You're a funny creature. What are you? A lawyer or a new kind of woman?
Hilda: By day I'm a lawyer, at night...well, you might be surprised.
Maria: Why don't you get married?
Hilda: Well, being single has it's points–at least no-one will ever murder me.
Paul: Tell me how do you think the case looks.
Hilda: Not too good. So many wife murderers have been acquitted on the same defense I fear the reaction. The jury is liable to doubt the existence of enough lovers to go around.
Paul: No, you're wrong, Hilda. No matter how low a woman may fall, there's always a man waiting for her.
Hilda: Then there's still hope for me.
Paul: For faith is the greatest element in love. And exclusiveness of possession is all that makes marriage worthwhile.
Paul: The greater the love, the greater the hate. The bitterer the illusion, the more serious the wound. The shrewder the woman, the more lustful the revenge. The more we love, the more we want to destroy the woman we've loved. Did the defendant love his wife so much that the murder can be explained by such love?
Hilda: Is it an acquittal?
Paul: What do you think, Hilda?
Hilda: As a lawyer, I congratulate you–you've probably won. As a woman, I didn't believe a word of your argument.
Hilda is my hero. I think.