En route to apply for a job as horse-trainer for Colonel Doon, ex-jockey Billy Decker rescues a girl on a runaway horse and discovers that she is Jennie Doon, the late colonel's daughter and manager of the stables. Jennie hires Billy to train Moonstone for the Kentucky Derby and approves of her brother, Johnny, as jockey. While the Doons work with Moonstone, Harvey Boyd places his hopes on his horse, Bluebell, the derby favorite, so that he may satisfy the demand of Amos Snivens that he repay certain loans. Boyd unsuccessfully offers to buy Moonstone and attempts to bribe Billy. While Billy and Johnny guard the stable, Boyd's men drug them and set fire to the building. Moonstone is rescued, Johnny is injured, and Jennie herself dons the family silks and arrives at the track in time to ride to victory. Boyd must answer to the sheriff for his tactics.—AFI