In 1850, during the California gold rush, physician-turned-gambler John Oakhurst delivers a baby girl but cannot save her barmaid mother. Because he believes that the orphan will bring him luck, John agrees to keep the girl, whom he names Luck, and raise her with his partner, the Duchess. Eight years later, Poker Flat, now a boom town, is invaded by the reform-minded Reverend Sam Woods and schoolteacher Helen Colby. Concerned for her future, John sends Luck, a tomboy cardsharp, to live with Helen and attend school. Then he forces brutish outlaw Sonoma and other gamblers in town to contribute to Woods's church fund as a way of quelling the town's reform movement. Soon after, Indian Jim, one of Sonoma's men, is killed in a saloon fight, and to avoid the creation of a vigilante committee and a lynch mob, Woods offers to warn John about controlling his lawless patrons. While Woods argues with John in his office, Luck, who has slipped away from Helen's house, plays poker in the saloon with Sonoma. When John finds Helen and Sonoma fighting over Luck, he screams at Helen to leave town, then during a confrontation with the outlaw, John is shot. Stunned by John's harsh words, Helen accepts Woods's marriage proposal and prepares to leave town with him, unaware that John's gunshot wound is serious. After Luck convinces her that John loves her, however, Helen joins Woods in a prayer for the gambler's recovery. Now recuperated, John openly pursues a romance with Helen and, as an endorsement of the reform movement, refuses to defend his honor in a duel with Sonoma. Outraged by his sudden pacifism, the Duchess tells John that his love for Helen is forcing him to behave against his true nature, and to prove her wrong, John kills both Sonoma and his cohort in a shootout. John, the Duchess and the saloon employees are then forced out of Poker Flat by a vigilante committee but are joined by the devoted Helen. While camped at a deserted cabin, the horses are stolen, and the group is stranded in a snow storm. When Luck, Woods and the rescue team arrive, they find the Duchess frozen to death, and Helen unconscious from the cold. Then in the woods, Woods and Luck discover a suicide note pinned to a tree and John's corpse beneath it.