Middle-aged bride Ann Hamilton soon begins to suspect that her charming husband is really a psychotic who plans to murder her.

Approaching middle age, spinster Ann Hamilton, the daughter of Science Professor David "Dink" Hamilton, is intelligent, but dowdy and unsophisticated; she never expects to get married and does nothing but be her tomboyish self in any effort to attract a man. Being single does not bother her and she repeatedly turns down the marriage proposal of Dink's colleague, Professor Joseph Bangs, whom she doesn't love. When she meets wealthy, handsome industrialist Alan Garroway, who is doing business with Dink, she's surprised that she likes him, then that they have a whirlwind courtship, fall in love, and marry. Alan made his wealth during the war in a family-started business that ended up being a parts supplier to the military for their aircraft. In their bi-coastal marriage--Alan's company's headquarters in San Francisco, while he grew up and still owns property in Middleburg, Virginia, outside of Washington, D.C., where he has many friends in high society--Ann begins to have doubts: she feels out-of-place in his high-society world, like she is a laughingstock among his friends. He is able to quell her fears about this issue as he acts as her guide to fashion and society behavior. More importantly, she feels that she doesn't really know Alan, mostly because he hid from her the fact that he has a brother, Michael, from whom he is estranged and whose current whereabouts he does not know. Michael was once part of the business in its early struggling days, but they parted when Alan caught him stealing from the company. Although she loves and trusts Alan, Ann begins to feel a kinship to what little she learns of Michael through her own investigation, which could place her at odds with Alan, and place her life in potential danger at either the hands of Alan or Michael, which of the two depending on if Alan is telling her the truth about his brother.—Huggo

Life is good for Ann Hamilton (Katharine Hepburn), living with her popular scientist father and poised to become a spinster scientist herself, until one fateful night she meets the inventor Alan Garroway (Robert Taylor) whose distance controller has revolutionized the aeronautics industry. Alan woos Ann and they marry in a whirlwind affair with Alan whisking Ann away to Washington to live. In Washington Ann realizes that she knows little of Alan's past, particularly his emotionally charged relationship to his brother Michael (Robert Mitchum), rumored to have bankrupted the company Alan and he had created. Michael is missing and has been absent for years with speculation by many that some dark activity may be connected to his disappearance. When people keep mentioning Michael to Ann she asks Alan and every time Alan responds with drama, at one point verbally abusing Ann for her interest in the brother. When Michael appears late one night to confront Alan about how he obtained his original plans and patent for the long-distance regulator that has made him a millionaire, Alan plans a method of revenge that includes another murder.