Margot Anstruther moves into an old New York brownstone and launches her career as a screen actress under the director Frederick Stoner. During a party celebrating her success, she shares a local ghost story about a vanished lodger, setting off a sequence of uncanny events. That night, she witnesses a severed hand extinguishing a dropped match from beneath her brass bed. Horrified yet analytical, she calls her friend and camera operator, Gene Valery, who finds nothing underneath.
Unconvinced, Margot enlists the police, leading to the discovery of a secret compartment in the flooring that conceals the mummified arm of Stella Ball, a former tenant who vanished months earlier. Alongside this gruesome find, investigators unearth a stolen radium tube linked to a high-profile theft from the Fellowe Institute. As the mystery deepens, Margot applies her scientific background and deductive reasoning to decode the physical and human evidence.
She realizes that Stoner is linked to the criminal underworld through a shadowy figure named Murchison, who had stolen the radium and sought Stoner to rent it for cinematic hoaxes. Stoner tries to manipulate Margot into dropping the investigation through intimidation and false theories, but she refuses to relent. Teaming up with actress Corinne Delamar, Margot confronts Stoner with his complicity, forcing his resignation. Meanwhile, the police capture Murchison, recovering the stolen radium and closing the case on the physical plane. Margot emerges triumphant, securing her future as a star while finding clarity in her romance with Gene.
