After the wealthy Mr. and Mrs. Ashby die in a plane crash, their three children are left in the care of their Aunt Harriet. Three years pass, and the eldest, Tony Ashby, jumps into the sea after leaving a suicide note, though his body is never recovered. Eight years later, the younger son, Simon Ashby, has grown into a cruel, spendthrift alcoholic who schemes to have his sister, Eleanor Ashby, declared insane so he can seize the entire estate.
Three weeks before the inheritance is due, a man who resembles Tony appears. At first, he is seen only by Eleanor, who believes her deceased brother is reaching out from beyond the grave. She even tries to help him during a suicide attempt, and the man insists he is Tony who simply ran away. Yet Aunt Harriet dismisses him as an impostor. In truth, this man is a conman hired by Keith Kossett, the son of the family attorney, to keep embezzling from the estate.
The impostor soon hears music from the family chapel at night. When he investigates, he is attacked by a masked figure with a hook. Eleanor heard the music before but was too afraid to leave her room. Simon appears to be open-minded about him but does not truly believe the tale. Fearing that he will lose the inheritance, Simon sabotages the car when the supposed Tony and Eleanor go for a drive, leaving Eleanor badly shaken.
That same night, the music resumes. Eleanor and the impostor explore and discover Simon at the organ, accompanied by a masked singer—only to realize the singing is a recording. The masked performer is unmasked as Aunt Harriet, who reveals that Simon has been driven insane by guilt over Tony’s death. The ceremony is a cruel ritual meant to calm Simon by letting him pretend his brother is still alive: Harriet, as a masked singer, provides Tony’s voice while Simon plays Tony’s part on the organ, and the impostor is invited to “join” Tony in the illusion.
Eleanor finds herself drawn to the impostor and wrestles with feelings that border on the forbidden. She nearly takes her own life, but he stops her and confesses that he is not her brother. Meanwhile, the nurse who cares for Eleanor’s health becomes involved with Simon; she suspects his murder attempt and threatens to reveal him, so he drowns her in the garden pond and tells Eleanor that the nurse vanished.
The impostor continues to investigate the chapel and uncovers Tony’s real, mummified body behind a hidden wall, despite Harriet’s attempts to stop him. When he tries to leave, Simon arrives and admits he manipulated the real Tony into writing the suicide note and then murdered him, sabotaging the car to cover his tracks. The impostor is restrained, and the truth begins to fracture the fragile lie.
As the impostor comes to his senses, Simon orchestrates one last grim tableau: he plays the organ with Tony’s body seated in a chair, and declares that the impostor will “join” Tony. Harriet reappears, urging Simon to withdraw, claiming she will handle the aftermath. She remains disturbingly unshaken by the corpse and even sets the chapel alight with a lantern to protect Simon, then exits.
Eleanor, alerted by the growing flames, returns and discovers the real Tony’s body. She frees the impostor, and together they flee the burning chapel. Inside, Tony’s remains burn with the building, and Simon’s madness finally erupts in the face of his own deception. He staggers toward the blaze, desperate to rescue Tony, but is overwhelmed by the flames and collapses as he clings to the skeletal remains of his supposed brother. The tragedy closes on a chilling note: a family’s wealth and ego collide with guilt, deceit, and the haunting certainty that some sins cannot be buried.
