A man murders his wife so he can be free to marry her sister.

The seemingly perfect marriage of Kathryn and Richard Mason is the envy of their friends, but on the day of their fifth wedding anniversary, the couple quarrels bitterly over Richard's infatuation with Kathryn's younger sister, Evelyn Turner. Later, at a party in the Masons' honor, which is being given by psychologist Dr. Mark Hamilton, the discussion turns to the nature of psychology. Hamilton explains that a thought can be like a malignant disease and it is his job to help a patient get rid of that thought. He adds that love is often at the root of psychological problems. On the way home, Richard loses control of the car and crashes. Kathryn and Evelyn come through with only minor injuries, but Richard suffers a broken leg. Later, although x-rays show that Richard's leg is healed, he insists that he cannot stand on it. When the doctor recommends swimming to strengthen the injured leg, Kathryn and Richard plan a trip to the mountains. At the last minute, however, work keeps Richard in town, and he sends Kathryn on alone, promising to join her the following day. On the way, Kathryn stops at Hamilton's to ask him to look in on Richard, and he presents her with one of his prize roses. Several miles from the lodge, Kathryn's road is blocked by another car, and Richard steps out of the fog and strangles her. He then pushes her car over the cliff and rolls a pile of logs on top of it. That night, he establishes an alibi with a business associate and feigns worry when Kathryn does not arrive at the lodge on time. When Hamilton telephones as Kathryn asked, Richard tells him that she is missing and then calls the Highway Patrol and institutes a search. He also notifies Evelyn, who has been staying with her mother. The police are unable to find Kathryn, but a short time later, a hobo is spotted trying to pawn her distinctive cameo ring. At home, Richard smells Kathryn's perfume in their bedroom and discovers her safe key on his desk. Richard frantically calls the police when he finds Kathryn's wedding ring inside the safe. Richard's response leads Hamilton to suggest that he and Evelyn accompany him to the mountains for some fishing. Hamilton also invites Professor Norman Holdsworth, a young doctor who is interested in Evelyn, to join them in the mountains. After Evelyn turns down Norman's proposal, Richard tells her how he feels about her. Although Richard insists that she rejected Norman because she returns his love, Evelyn vehemently denies this. Richard returns to his office for a day, where a letter addressed in Kathryn's handwriting and containing a pawn ticket is waiting for him. He traces the ticket to a pawnshop and finds Kathryn's locket. When he brings the police to the pawnshop, however, the locket is no longer in the case, and the pawnbroker denies Richard's story. Then, Richard sees a woman he believes to be Kathryn and follows her to an apartment house before losing her. Richard visits Hamilton's office to ask his advice and is told that the psychologist can do nothing for him. Desperate, Richard drives back to the scene of the crime. The pile of logs is still on the car, so Richard climbs down the mountain, where Hamilton and the police are waiting. Hamilton explains that he knew Richard was lying when he said Kathryn was wearing a rose when she left the house, because Hamilton had given her the rose himself. The police found Kathryn's body the day after the murder, but because there was no proof of Richard's guilt, they agreed to stage Hamilton's trap and let Richard's own fears convict him.