When jockey Jimmie Driscoll, responsible for making Jim Richardson's horses winners, is fired for being too heavy, he goes to the home of the late Judge Bell, the father of local horse racing. Jimmy is in love with the Judge's daughter Joy, who was left nearly penniless when her father died. Joy's brother Harry writes to her pleading that because he desperately needs money, she should enter the aging Vagabond, the last of the Bell racehorses, in the upcoming annual event. Convinced by crooked bookmaker Spike Bradley that Vagabond will win at twenty-to-one odds, Harry mortgages his half of the house for gambling money. Jimmie discovers that although Vagabond runs horribly on normal turf, she is a "mudder," meaning that she goes into a wild dash on wet ground. After Jimmie and Joy pray for rain, Bradley, learning of Vagabond's condition, threatens the jockey, but Jimmie, riding Vagabond himself in in the rain, wins the race and afterward, Joy's love.