Jack and Dolly, his sister, live together in the west. On Jack's birthday, Dolly presents him with a peculiar ring. The brother and sister attend a masquerade ball that evening, each dressed in the other's clothes. Dolly, being taken for a man, meets Big Bill, a new ranchman, and he offers her a cigar, which she tries to smoke. Jack sees her in distress, and coming to her rescue, is introduced as the sister. The next morning Jack leaves to look over his stock. While riding through the sage brush, he takes a shot at a rabbit and the bullet lands near the spot where a cattle rustler is plying his unlawful trade. The cattle rustler and Jack meet. The former believes that Jack tried to kill him and a fight follows. Jack is killed. The murderer takes all Jack's money, including the ring. After two weeks of search the sheriff and his posse return without having seen the murderer and so report to Dolly. She determines to run the man down herself and sets out disguised as a cowboy. Her funds soon run low, however, and she is forced to seek work to carry on her search. Dolly approaches a ranch house and meets the owner, who is Big Bill, and as he has taken a liking to what he thinks is a young fellow, he gladly gives her a job. In the days that pass, Big Bill begins to doubt the sex of his new employee, but keeps his suspicions to himself. One day he asks the cowboy to accompany him to town, and while there, Dolly wanders into a saloon to watch the games in progress. Bill follows, keeping a close watch. Suddenly one of the players who is heavily losing, pulls out a sack and empties its contents on the table. Dolly receives a shock when she sees the ring she had given Jack, and at once guesses his identity. Dolly denounces him and they have a terrific fight. Bill tries to interfere, but the boys, thinking she is a man, hold him off. In the melee, Dolly's hair comes down and her sex is revealed. The fight is quickly stopped and Dolly tells of the murder. The rustler is delivered to the sheriff, and Big Bill takes Dolly home, where he offers her a new job as boss of his ranch.