And so the mystery of the midnight train has been solved. Si and Elmer, the two correspondence school detectives, failed to solve the case alone, but with the help of the Sheriff, the old lads have finally made an arrest. Our scene is now the rancho of Don Jose Tijuana, the last of the great Mexican ranchers. It is daylight, and Si and the Sheriff are patting themselves on the back for a good night's work, while Elmer is nowhere to be seen...