Carol wins the lottery, but unfortunately her sudden wealth leads to a disagreement with her fiancÃ© Ronald, and the two break up. Carol quickly falls in love with the romantic and mysterious Gerald, and marries him despite the warnings of her friends. It is not long before Carol begins to see that Gerald is disturbed and perhaps even dangerous, and she soon realizes that she is in great peril.
Carol Howard (Ann Harding) is young woman who works in London at a very ordinary clerical job. She wins a fortune, ninety thousand pounds, in a French lottery. According to what we find later, this is 36 times the price of a nice cottage in the country. She walks off her job and returns to her modest apartment to talk to her best friend Binnie Hale (Kate Meadows) and her elderly aunt Lou (Jean Cadell), who uses complaints about her health to get a bit of loving attention. Carol wants to have luxury and fun with her money for a while, and postpone worrying about her future.Carol's fiancé Ronald Bruce (Bruce Seton), after years of hard work, is just about to get a promotion, and does not want to give that up. His refusal to quit his job causes disagreements and they break up.Carol makes living arrangements for Aunt Lou and puts her flat on the market for rent prior to leaving for France to collect her money and travel in luxury. Cultivated bachelor Gerald Lovell (Basil Rathbone) shows up to inspect the flat and says it is just what he needs. He claims to be a wealthy chemical engineer with a passion for his photography hobby, and he takes the modest flat although he could afford something much more expensive, explaining it reminds him pleasantly of his youth.As Carol and Kate get on the boat to go to Paris, they find Gerald is on board. Gerald now turns on the charm, and Carol quickly falls in love with the romantic and sophisticated man, who is a connoisseur of food, art and Paris.Some time later Ronald comes to Paris and seeks out Carol in her luxurious dwelling, having had second thoughts about their breakup, offering to change his work plans, but it is too late. Carol has married Gerald, despite warnings from Kate.Indications that Gerald has major things to hide begin as the couple makes plans to return to England. Gerald claims that bureaucratic problems with his bankers make it necessary for him to borrow five thousand pounds to make the purchase of a charming secluded country cottage, and he gets Carol to sign legal documents without reading the details.As they move into their cottage, Gerald insists on setting his darkroom in the basement, and has strict orders that no one should ever enter it, on the excuse that there are dangerous poisonous chemicals around. Gerald's violent anger when a servant puts a package inside the basement, or when Carol comes in to talk to him there, indicate he is disturbed and possibly dangerous.In the following weeks, Gerald succeeds in isolating Carol so she has no one to talk to. Then he announces that on the day of the town fair they will be leaving for a long trip to a location that only he knows. He shows signs of illness, and Carol insists that he see the local doctor, despite loud protestations from him that doctors are all quacks, and he will refuse to take any medicines.At about this time Carol hears from the servants that the cottage they live in was priced at two thousand five hundred pounds, not the five thousand that Gerald had borrowed. When Gerald hears about this discrepancy, he goes into an angry tirade. At this moment Carols attitude switches from idyllic honeymoon to fear.When Dr. Gribble (Bryan Powley) examines Gerald, he diagnoses Gerald as having a serious heart condition that threatens his life unless it is treated. Gerald dismisses Dr. Gribble completely until the doctor happens to notice a book that Gerald has been reading that denotes a serious interest in criminology. They strike up a conversation on the book and the criminal case histories in it, focusing on Fletcher, a serial murderer of wealthy women who has avoided conviction. Gerald waxes lyrical, enthusiastic and admiring in talking about Fletcher's accomplishments. As Dr. Gribble examines the book section on Fletcher, he says he has the same book at his home but it must be a different printing, as his book has a photograph of Fletcher. The doctor offers to bring his own copy of the book some time, but Gerald says some other time, as they are leaving for a long trip in the following morning.Ronald and Kate show up at the cottage, sensing that something may be wrong. Carol is very happy to see them and wants to invite them to stay for dinner, as she has arranged for a celebration dinner of sorts with the maid Emmy (Joan Hickson). But when Carol goes upstairs to tell Gerald about it, he goes berserk and yells angrily that he won't put up with them for one minute.As Carol is saying a slow good bye to Ronald and Kate, Dr. Gribble comes back to the house with his own copy of the criminal case histories book. A comparison with his copy shows that the portrait of Fletcher has been torn from Gerald's copy. Fletcher has a beard and is blond, while Gerald has a small mustache and is black haired, but we the viewers can recognize him. Carol comments that he does look vaguely familiar.Dr. Gribble leaves, Gerald comes down the stairs and, after dismissing Emmy for the night and until they return, proceeds to lock all doors of the house. By this time Carol becomes very concerned about her own safety as Gerald's psychological problems are increasingly manifest. In order to gain time she goes ahead with the planned elaborate dinner, and in her conversations she is both verifying her worst fears that Gerald is Fletcher and intends to kill her shortly, and planning some sort of escape.As the conversation proceeds, it gets ever more intense, and Gerald notices that a sort of confession is being wheedled out of him. He confesses that he learned that Carol had won the lottery from the agent who was offering the apartment for rent. Leaving little unclear, he talks about why he has murdered several women, his attitudes that no woman could ever match his intellect. Carol in desperation claims that she herself is a murderer that got away with it. As Gerald demands to know more and more details of what and how and why of her murder, just at the moment when he finally decides that she is lying, and he announces triumphantly that he doesn't believe her, she tells him that his coffee has been poisoned, and that she is just making time until he drops dead. She points out to him that she has not taken any coffee at all, and she stares at him.Gerald, taken aback, rises, his weak heart gives out, and he collapses to the floor.Miraculously, at this time, Dr. Gribble, Kate and Ronald arrive, with help from others they break into the locked house, and all is well for Carol at the end.