In the late nineteenth century, while sailing from Jamaica to Liverpool, England, missionary widow Olivia Harwood nurses artist Mark Bellis, who is suffering from malaria, the same disease that claimed her husband. Mark survives his illness and after returning to England, visits Olivia in the humble home she has inherited. Mark, a thief and murderer who is being hunted by Scotland Yard, flatters Olivia and plays on her vulnerability until she agrees to take him in as a boarder, even though she finds the idea of an unmarried man living with her scandalous. Soon after, Mark and his partner in crime, Edgar Bellamy, attempt to rob a new art collection being brought in by Lord Milbury, but are forced to escape without the paintings. Although she has other boarders, Olivia caters to Mark, who paints a portrait of her and subsequently makes love to her. When Mark tells Olivia that he must leave the country because he is broke, she seeks out her childhood friend, Susan Courtney, who has married a wealthy Peer. Susan's opulent lifestyle has not saved her from the misery she feels because she is childless, however, and has become an alcoholic. Susan gives Olivia her housekeeping money, which Olivia turns over to Mark. When Olivia tries to burn a packet of letters that Susan wrote to her while in Jamaica, telling of her love for Sir John Curle, the Queen's counsel, Mark snatches the letters, and encourages Olivia to be more self-serving. Olivia's love for Mark is so strong that she almost agrees to blackmail her friend, but instead runs to the Anglican Missionary Society and begs them to send her out of the country. The Society's representative only offers Olivia a chance to remarry, and she then seeks solace at the church, where Mark finds her and consoles her. Later, Susan's husband Henry offers Olivia a paid position as Susan's caretaker, hoping to keep his wife from drinking. Olivia enjoys being pampered as Susan showers her with new clothes, while Mark continues to see his lover, Kitty Feathers, and gives her Olivia's locket as a gift. When Henry suffers a high blood pressure attack, Olivia eases his pain with some Jamaican medicine. Henry later admits to his domineering mother that it is he who is infertile, and leaves to see a specialist in France. While he is gone, Olivia encourages Susan to write to John, and Mark sells Susan's bonds anonymously. Unknown to Mark, he is followed from the stockbroker's office by a detective named Jarvis. Henry returns unexpectedly and confronts Susan and Olivia about the bonds. Unimpressed by their weak response, Henry arranges for Susan to go to a sanitorium and dismisses Olivia. Olivia later blackmails Henry with Susan's letters to John. Henry insists that Jarvis, whom he hired, not alert Scotland Yard until he plays out his scheme to entrap Mark, whom he now knows is a notorious criminal. That night, Henry shows Olivia the detective's report on Mark, and demands the letters in exchange for the report. Olivia is shocked to learn that Mark is a murderer as well as a thief, and when Henry tells her the original report is with Scotland Yard, she hits him. Henry collapses from a heart attack, and Olivia puts poison in a bottle of medicine, then urges a hysterical Susan to tend to her husband. Henry dies of poisoning, while Olivia burns Susan's letters. Olivia then meets Mark at the train station for their flight from the country, and when he hears what has transpired, he insists that she stay behind and act like Susan's faithful friend so as not to arouse suspicion. Mark, meanwhile, flees to Paris with Edgar. Susan is found guilty of Henry's murder and slowly goes insane. Olivia is surprised one evening by a visit from Jarvis, who appeals to her to confess and thereby spare Susan's life. Tormented, Olivia writes to Mark about her own confusion. Having genuinely fallen in love with Olivia, Mark returns to England, where he convinces Olivia not to confess and promises to take her to the United States the next day. Before Olivia leaves, Jarvis sends Kitty to her house, and Olivia is stunned to see her locket around Kitty's neck. Olivia then meets Mark as arranged in front of Westminster Abbey. Mark admits that his first interest in her was purely mercenary, and then professes his sincere love for her. Olivia, reeling from the shock of his duplicity, stabs him to death, then directs the cab driver to the police station. When she exits the cab, she discovers that Jarvis is the driver, and he congratulates her for her courage.