Oil is discovered on the Countess de Elberca's estate in a mythical Spanish American country. Mercedes McDonald, her niece, falls in love with Sandy Buchanan, a young Scotch engineer hired by the countess. Don Felipe, a neighbor in need of money to avoid arrest for embezzlement, conspires with his nephew, the Duke of Othomo, for the latter to wed Mercedes. The aunt approves the suit. Felipe and Othomo attempt to kill Mercedes' sweetheart, but Buchanan, with the aid of her brother and a traveling American circus, foils their plans. Felipe and Othomo are killed by the circus animals, and the aunt consents to Mercedes' marriage to Buchanan.

Lucy Bostil, daughter of a Colorado ranch owner, is led by a dog to his master, Lin Slone, who is exhausted from a struggle to capture a wild horse; she revives Lin and they christen the horse "Wildfire." The Bostils have entered Sage King in a race, but Lucy agrees to tame and train the wild horse, since Buckles, her favorite colt, has been stolen. When Joel Creech, a half-witted stable hand, is discharged, he becomes a tool of the Cordtses--who also have entered a horse (Buckles) in the race--in drugging Sage King. Lin and Lucy enter Wildfire under the Bostil colors, and she rides him to victory, When Cordts is disgraced and discovered to be a horse thief, he persuades Joel to abduct Lucy. Joel does so, but first he kills Cordts. Warned by his dog of Lucy's danger, Lin pursues and rescues the girl.