Eileen Meredith receives word from an "unknown friend" to call at the house of her fiancé, Robert Grell, where she will discover something of great importance. Unable to go, Eileen sends her sister Helen in her place. Helen enters the library where she finds a dead body resembling Grell. The real Grell then enters and, seeing Helen holding the dagger, mistakes her for Eileen and flees, hoping to cast suspicion on himself. Criminologist Heldon Foye takes the case. Foyle is in love with Helen, and when he finds her prints on the dagger, finds himself in a struggle between love and duty. Meanwhile, Grell locates the real murderer, a woman who clears up the mystery by explaining that the murdered man was Harry Goldenberg, her husband and Grell's dissolute brother who had come to blackmail him. In a struggle, she had stabbed Goldenberg, but because she had worn gloves, no fingerprints were visible on the dagger. The mystery thus resolved, Grell marries Eileen while Helen forgives Foyle for misjudging her.

Director:
Paul Scardon	Director
Cast:
Earle Williams	as Heldon Foyle
Miriam Miles	as Helen Meredith
Jean Dunbar	as Eileen Meredith
Denton Vane	as Robert Grell/Harry Goldenberg
Mabel Trunnelle	as Lola
Frank Crayne	as Ralph Fairfield
Bernard Siegel	as Ivan
Robert Gaillard	as Detective Green
Cinematography:
Robert A. Stuart	Camera
Writer:
Graham Baker	Scen

The actress who played Eileen Meredith was listed variously as Jean Dunbar and Jean Dumar.

Based on the novel The Grell Mystery by Frank Froest (London, 1913).