On her wedding day, Celia Barrett reflects upon the events that brought about her hasty marriage: When Celia's older brother Rick dies, she is left a large trust fund which the family lawyer, Bob Dwight, manages. Although Bob is romantically interested in Celia, she decides to go to Mexico with her friend, Edith Potter. One afternoon Celia and Edith witness a knife fight between two men over a woman. Celia is enthralled with the scene and attracts the attention of an American architect, Mark Lamphere. They find themselves drawn to each other and within days are preparing to marry. After the wedding, Mark tells Celia about his work managing an architectural journal and his fascination with reproducing in exact detail rooms in which brutal murders were committed. The couple's honeymoon is abruptly interrupted when Mark tells Celia he has received a telegram summoning him back to New York City. Mark asks Celia to go ahead to his family estate in Lavender Falls, where he will meet her later. That night the maid disconcerts Celia by telling her Mark received no telegram. Puzzled, Celia nevertheless proceeds to her new home, where she is met not by Mark, but by his sister, Caroline "Carey" Lamphere, who informs her that Mark has been delayed. Once at the house, Celia is shocked to discover Mark has a young teenage son, David. Carey introduces Celia to Mark's secretary, Miss Robey, who wears a scarf to cover the side of her face that was burned years before when she rescued David from a mysterious fire. When Celia meets Mark at the train station, he reacts oddly to her lilac corsage. Later he tells Celia he is worried about money, as his journal is failing. During a large party thrown by the Lampheres, Bob tells Celia he believes that Mark may have married her for her money. Mark then takes the guests through his recreated rooms, which feature shocking murders of wives by their husbands, and Celia is mystified when he angrily refuses to show her the last room, which remains locked. A few days later Celia breaks up an argument between Mark and David. David later tells her not to interfere, as he will never get along with Mark, who he believes murdered his mother. When Celia asks Mark how his first wife died, he refuses to tell her and grows detached and cold. Determined to get into the locked room, Celia searches for the key in Mark's workroom, where she discovers Miss Robey without her scarf and with no sign of a scar. Miss Robey admits she had the scar removed years earlier, but feared being fired by Mark, who knew she was in love with him, if he realized she was no longer disfigured. Later, Celia finds the key to the locked room and makes a wax impression of it and has a copy made. When Celia enters the mysterious room she realizes it is an exact replica of her own bedroom, and is certain Mark means to murder her. She tries to run away, but returns the next morning determined to help her husband. Mark, meanwhile, fires Miss Robey and Carey decides to move into town. Shortly thereafter, when David has left for school and Celia and Mark are alone, Celia goes to the locked room and awaits Mark, who soon arrives, set upon killing her. Celia forces him to recollect a series of traumatic events from his childhood that have led him to this mental breakdown. As Mark comes to the realization he is not a murderer, the two find that the house is on fire, having been set ablaze by a jealous Miss Robey. Mark and Celia just manage to escape and, freed of their suspicions of each other, determine to start a new life together.