Montana cowboy Duke Fergus comes to San Francisco in search of restitution from wealthy gambling house owner, Tito Morell, for a horse sale. Duke meets Ann "Flaxen" Tarry, unaware that she is Morell's girl friend and star performer at his Eldorado gambling house, the center of the notorious Barbary Coast district. At the Eldorado, Morell informs Duke that he paid for the horse in full and was not responsible for Duke's representative later losing the money gambling. When Duke accuses the Eldorado of being crooked, Morell pays him the amount due, then Flaxen takes him through the gambling tables and on to several neighboring houses, ensuring his win on every bet. Later, the other proprietors complain to Morell about their heavy losses, so he repays winnings that Duke acquired in a fixed card game. Embarrassed at his losses, Duke leaves town to continue his cattle drive, only later realizing he has been conned by Flaxen and Morell. After he sells his herd, he visits old friend and cardsharp Smooth "Wolf" Wylie and asks him how to beat Morell's system. Duke then returns to the Barbary Coast with all his money and Wylie to challenge Morell. He plays Morell and the other gamblers, soon winning enough money to begin construction of his own beach front house and a new club, called the Silver Dollar. Meanwhile, the city newspaper editor, Cyrus Danver, tells Morell that the political climate is against the rapid rise of the area gambling houses and elections will soon drive them out. Duke attempts to outbid Morell for Flaxen's contract, and when she uses the opportunity to raise her benefits, Morell refuses to go along. They quarrel and Flaxen agrees to sing for Duke at the Silver Dollar. Duke meets with the other gambling house owners, and suggests they incorporate and run a clean and legal business. On the night of the Silver Dollar's opening, Morell attempts to win Flaxen back to the Eldorado and threatens Duke, but is overpowered by Wylie. After Flaxen's performance a great earthquake hits the city and the ensuing fire destroys much of the Barbary Coast including the Silver Dollar. Duke carries Flaxen to safety after she is hurled from the stage, but she is left paralyzed from her fall. Morell comes to visit her, but is disappointed by her injury and is more concerned with rebuilding and enlarging the Barbary Coast than her health. When Morell gets behind a shady challenger in the mayoral elections, the city business representatives ask for Duke's support. Dismayed over his losses, Duke refuses, planning to return to Montana. When Morell unexpectedly approaches Duke with the same suggestion of incorporating the gambling houses but for illegal purposes, Duke is angered and agrees to stay and fight for the city. Flaxen, hurt by Morell's rejection, determines to walk and on the night of the election, manages to walk into the Eldorado. Morell, waiting for illegally gotten tally sheets to rig the elections, is impressed enough to offer Flaxen her old job back. Duke and the election officials arrive in time to seize the tally sheets, and later, Flaxen leaves with Duke for Montana.