Paul Sturgess is engaged to Grace Van Austin. At a weekend party in their Newport home, Grace amuses herself by flirting with one of their guests, Howard Esterbrook, a man of unusual charm. This arouses Paul's jealousy and precipitates a desperate fight between the two men. They are separated by the others, and that night Stephen, a servant, sees Paul try to enter Esterbrook's room, revolver in hand. Paul is interrupted by a maid on an errand, and hurries to his own room. Fearing for Esterbrook's safety, Stephen enters his room to warn him and sees a hand extend through the window curtain, stab Esterbrook, and mysteriously disappear. At the investigation, Paul is arrested on circumstantial evidence. Six months later, Ann, "The Woman of Mystery," is taken with a number of other prisoners in a raid, during which she is shot by Renway, a criminal, while trying to aid the police. Greatly stirred by hearing that Paul Sturgess's plea for pardon has been denied and that he must die in the electric chair at dawn, the woman tells Detective North, leading the raid, something that causes him to rush her to the District Attorney at once. There she tells her story again and the Warden at Sing-Sing is telephoned just in time to stop the electrocution. The District Attorney and Ann start for Sing Sing. In the Warden's office, in the presence of the District Attorney and the prisoner, Ann tells how she killed Howard Esterbrook, and the powerful reason why. In the course of her story it is revealed she is the mother of Paul Sturgess. At the completion of her narrative, Ann dies in her son's arms. Completely exonerated, Paul returns home, and is happily reunited with Grace, who had retained faith in his innocence throughout.