In 1903, kindly London tobacconist Philip Marshall lives on Laburnum Street with his adult son John and his shrewish wife Cora. Unable to stand his mother anymore, John moves out and Philip takes this opportunity to move into his son's old room. Later, Philip takes pity on Mary Gray, a young, out-of-work stenographer, and invites her out to dinner and finds her a job as a dress shop model. The two soon begin seeing each other regularly, although she is unaware that he is married. Returning home late one evening, Philip finds his bedroom door locked, forcing him to confront Cora and ask for a divorce. She refuses and threatens to ruin his good name if he leaves her. Philip then confesses all to Mary and ends their relationship. That Christmas, Cora tells her husband that she knows all about Mary, and even though Philip tells her that he is no longer seeing the young woman, Cora informs him that she still intends to have Mary fired from her job and evicted from her boardinghouse. Seeing no other alternative, Philip kills Cora. Although the coroner rules Cora's death an accident, Inspector Huxley of Scotland Yard begins an investigation of the case and correctly deduces that Cora was struck in the back of her head by a cane, and did not receive the wound by accidentally tripping down a flight of stairs, as previously assumed. With no incriminating evidence against Philip, Huxley looks for a motive and soon finds one when the tobacconist begins seeing Mary again. Huxley's investigation is stymied, however, when Philip and Mary wed, and, under English law, she cannot be forced to testify against her husband. Philip and Mary's marital bliss is later disrupted when Gilbert Simmons, their snobbish neighbor, informs Philip of his intention to falsely testify against him unless he is paid for his silence. Realizing that Gilbert will blackmail him into bankruptcy, Philip kills him by placing an overdose of Bayard's Anodyne in his whiskey. With two murders haunting him, Philip then convinces Mary to move to Canada, where they can join John, who has a new job there. She agrees, but just as the couple is boarding the ship to North America, Philip is informed by Huxley that Gilbert's body has been found and his abused wife Edith has been charged with his murder. Unwilling to let another suffer for his crimes, Philip gets off the ship and slowly heads toward Scotland Yard to turn himself in.