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During the search for bodies among the wreckage of a boat lost in a storm near Hawaii, detective Charlie Chan finds a diary of Alan Coleby, heir to his father's fortune, which indicates that he was on board and that attempts had recently been made on his life.  Chan cables Henrietta Lowell, matriarch of the family and the sister of Alan's deceased father, that Alan's fate is uncertain and flies to San Francisco where Mrs. Lowell, a devoted believer in "psychic research," schedules a séance.

Alan returns to the Coleby estate, but upon entering, he is hit by a thrown dagger.  The séance is conducted by Carlotta, a medium, and attended by her husband, Professor Bowan, whom Mrs. Lowell supports financially; Mrs. Lowell's two daughters, Alice and Janice; Alice's boyfriend, newspaper reporter Dick Williams; Janice's husband, Fred Gage; Ulrich, a disgruntled servant, who blames his daughter's suicide seven years earlier on Alan for breaking his engagement with her; and Chan.  Alan's face appears in the darkened room, and when the lights are turned on, Chan discovers that Alan has been murdered.  Chan arranges with Mrs. Lowell to spend the night in the house, which has many secret panels and passages, to investigate.

Curious, Mrs. Lowell sneaks away from her home to join Chan in his search for clues.  They find a radio receiver, which, Chan surmises, may account for the music they heard during the séance.  They also discover that Alan's image appeared when a hidden ultraviolet light was directed toward his face, which was covered with quinine sulfite, a solution that glows when hit by ultraviolet light.  Greatly upset, Mrs. Lowell reveals that Professor Bowan knew that if Alan were to return, her patronage would cease.  As she agrees with Chan's suggestion that she revise her will, now that she is the legal heir, a shot is fired at her from a hidden doorway, but Chan pushes her out of the way.  Just then, Gage enters the house and says that he came because he feared for his mother-in-law's safety.

The next day, after seeing a radio transmitter in Ulrich's room, Chan visits Carlotta, who admits the use of the transmitter.  She is shocked, however, to learn about the ultraviolet ray.  When Chan touches her shortwave coil, Bowan switches on the current, which causes Chan to fall unconscious.  Just then, the police arrive, but Bowan escapes.  Inspector Morton arrests Carlotta as Chan is revived.

Later that day, Mrs. Lowell announces to her family that she plans to sign a new will, which her executor Warren T. Phelps will bring at 8:30 that evening.  As the church bells ring at 8:30 and Phelps drives up, Mrs. Lowell is shot through the window.  Chan investigates the bell tower and finds a high powered rifle, which had been set to fire at the window when the bell was rung.

After Bowan is caught, and he does not confess, Chan calls all the attendees at the first séance back and has Carlotta conduct a new one.  When Mrs. Lowell's animated image appears, and it starts to speak, a dagger is thrown at the image, which cracks as the mirror on which it is reflected breaks.  When the lights are turned on, Chan reveals that Mrs. Lowell is alive and that a dummy was earlier shot.  Gage accuses Ulrich and they struggle, but Chan, who had put graphite on the knife, reveals graphite on Gage's hands and accuses Gage of murdering Alan Coleby to cover evidence of forgery in the Lowell accounts.  After Gage is led away, charges are dropped against Carlotta and Bowan, who agree to leave town, and Chan plans to return to his large family in Honolulu.