Robert Lanning, a proper Bostonian who owns an estate in southern New Mexico, suspects that some of his employees are smuggling arms into Mexico, and sends his son, Robert Jr., to investigate. During his journey west, Robert meets Mary Hamilton, a stranded actress from a roadshow company of Uncle Tom's Cabin. Because Mary is still in costume as the character, "Little Eva," Robert mistakes her for a child and takes her with him to the ranch. He ultimately discovers the identity of the arms smugglers and, with the help of the Mexican Rurales, brings the gang to justice. Robert then realizes that Mary is not a child and wins her for his wife.