Federal agent John Wyatt is assigned to a counterfeiting case for which suspicion has fallen on Dr. Carter, an ex-convict and proprietor of a roving medicine show. John trails the show to Arizona, where he helps the performers escape creditors by crossing the state line. Working undercover, John joins the show and meets Carter and his daughter Linda. The gang of counterfeiters is located in the border town of Las Riebes and is headed by Curly Joe Gale, Carter's former associate, who previously framed Carter for counterfeiting. By coincidence the show travels to Las Riebes. In town, Carter peddles his cure-all, "Dr. Carter's Famous Indian Remedy," backed by show members Mike and Ike's musical accompaniment. John displays his sharpshooting skill in an act he has prepared with Linda. The Mexican police force known as the Rurales investigate Curly. Trigger plants incriminating evidence in the Carter trailer which is later found by the sheriff. Although John escapes arrest, Carter and Linda are abducted by Curly's men. John identifies himself to the Rurales captain, and attempts to arrest Curly, who escapes during a scuffle. Manuel, a Rurales officer, finds Curly's secret cave and directs John to Curly's mine where Carter and Linda being held. Curly is about to shoot Carter when John surprises him and a fistfight ensues. The Rurales ride up just in time and capture Curly's gang. John takes Curly into custody for sentencing in the United States. Carter and a justice of the peace later get drunk on the Famous Indian Remedy, while Linda and John wait to be married.