An insurance investigator's ex-girlfriend draws him into a web of blackmail and murder.

After a fitful dream, London insurance investigator Oliver Branwell muses about an incident that occurred in the second year of his tenure at the Abercrombie insurance company: On Christmas Eve, Oliver is sent to Louis Manor, an estate owned by Tracey Moreton, to assess the damage caused by an electrical fire. Oliver is greeted by Tracey and his cousin and neighbor, Clive Fisher. After Tracey introduces Oliver to his wife Sarah and his mother, he shows him a valuable landscape painting that was damaged in the fire and invites him to stay for dinner. Although Sarah and Oliver were sweethearts five years earlier, and have not seen each other since, they pretend never to have met before. Several days later, Oliver surprises Sarah outside her London office and insists that she join him for coffee. When Oliver accuses Sarah of walking out on him, she protests that she was forced to leave after her father was threatened with prosecution for issuing worthless checks. Sarah and Oliver were each too proud to contact the other, and hence, Sarah met and married Tracey. Several months after his meeting with Sarah, Oliver is sent by his firm to convince recalcitrant film star Charles Highbury, who is suffering from a black eye, to return to work. After Highbury haughtily dismisses Oliver, Oliver overhears the actor's secretary speaking to a Mrs. Vere Litchen and decides to pay the lady a visit. At Vere's apartment, Oliver notices a landscape painting hanging on the wall similar to the one destroyed in the Moreton fire. He also learns from the flirtatious Vere that Highbury's wife gave him the black eye after she returned home unexpectedly and caught him with Vere. Oliver uses the information to embarrass Highbury into returning to work. Several months later, Clive brings Tracey, who is suffering from an asthma attack, to Oliver's office. Tracey explains that he is too ill to keep his date with Sarah at the theater and asks Oliver to go in his place. After the performance, Oliver and Sarah are caught in a rainstorm and Oliver insists that Sarah come to his apartment to dry off. There, Sarah casually questions Oliver about how to set a fire, and he asks her if she loves her husband. After Sarah explains that Tracey needs her, Oliver drives her home, where Tracey insists that he spend the night. The next day, as Sarah gives Oliver a tour of the estate, he recognizes the view as the landscape depicted noth in Vere's painting, and the painting that was purportedly destroyed in the fire. Upon returning to the city, Oliver goes to question Vere and is greeted by Willis Croft, her wealthy American fiancé who owns the apartment and its contents. When Willis describes the woman who sold the painting to him, Oliver becomes convinced that the woman was Sarah. Upon learning that Tracey, Sarah and Mrs. Moreton have decided to vacate Louis Manor while the fire damage is being repaired, Oliver drives to the empty house to ascertain if the paintings in Tracey's collection are forgeries. After sneaking in, Oliver stumbles over Tracey's dead body at the foot of the stairs and notices the railing that Tracey broke as he plunged to his death. Seeing smoke billowing from under the cellar door, Oliver hurries to the basement and finds a fire started in the exact method he described to Sarah. As Oliver phones the police, flames engulf the house, forcing him to jump out a window just as the fire brigade arrives. Upon returning home, Oliver falls into a fitful sleep until he is awakened by a phone call from Michael Abercrombie, his employer, notifying him about Tracey's death and the fire at Louis Manor. Several months later, Oliver receives a letter from Sarah informing him that she is the sole beneficiary of Tracey's insurance policy. When Sarah comes to visit soon after, Oliver accuses her of setting the fire and selling the painting to Croft. After Sarah storms out in indignation, Oliver goes to see Croft to show him Sarah's photograph. When Croft states that Sarah was not the woman who sold the painting, Oliver apologizes to her and they reconcile. Upon learning of Tracey's insurance fraud of the painting, Sarah insists on returning the settlement. Oliver proposes and on the day that they are wed, they go to Michael's office to return the check. Michael is away, however, and so they leave on their honeymoon without returning the money. Several days later, Sarah receives a letter containing Tracey's ring. Alarmed, they immediately return home. Soon after, Sarah is contacted by a Mr. Jerome, who tells her that his client has proof that the fire at Louis Manor was fraud and demands half the settlement for his silence. Jerome instructs her to meet him that night with her answer, but when the blackmailer fails to appear, Sarah nervously decides to take her dog for a walk. After she leaves, Sgt. Barnes and Det. Con. Watson come to question Oliver about the fire. When Oliver determines that the police suspect him and Sarah of setting the fire, he realizes that returning the check would make them appear even more guilty. The next day, Jerome phones Oliver at his office and sets up a meeting that night at the bandstand in the park. That evening, Sarah and Oliver hide in the park, and when Jerome leaves, they follow him home. There, they find a woman fitting Sarah's description and a stack of forged paintings. At that moment, Clive arrives, admits that he was the mastermind behind the forgery scheme and demands money for his silence. When Oliver and Sarah return home, they discover the dog is missing and Oliver finds a burning cigarette butt in the ashtray which he then extinguishes and stuffs his pocket. The next day, Oliver is summoned to Michael's office, and when he sees Barnes there, assumes that the detective has accused him of fraud. After handing Michael Sarah's insurance check, Oliver indignantly proclaims his innocence and departs. Meanwhile, Sarah has found the cigarette butt in Oliver's pocket and leaves a note informing him that she has gone to Louis Manor. Upon finding the note, Oliver hurriedly drives there and finds Sarah arguing with Mrs. Moreton, who has admitted that she took the dog and sent the ring. Mrs. Moreton explains that on the night of Tracey's death, she returned to the manor, suspecting that her son was planning to set another fire. When she confronted Tracey, he ran up the stairs in a rage, fell against the railing and plunged to his death. After Mrs. Moreton tells her story to a board of inquiry, Oliver insists on resigning from the firm as a point of honor, but his colleagues prevail upon him to stay.