Cowboy Roy Rogers (Roy Rogers) travels to Rancho San Angelo, a territory on the American-Mexican border, to help Cookie Bullfincher (Andy Devine) investigate some mysterious deaths around a silver mine. Roy's suspicion of mine manager Gus Ulrich (David Sharpe) is shaken by the unexpected arrival of Western author Lee Madison (Dale Evans), who advises Roy to read one of her books to help him solve the murders. Meanwhile, Cookie follows Ulrich to the mine and discovers a complex scheme.