On the very day of their graduation from the mail order college, these two ancient and rheumatic investigators were thrown into the middle of the biggest mystery ever known, in the sleepy little town of Punkenville. A stranger in the town was seen going into the bank, but when the detectives arrived on the scene, the stranger was gone, and the cashier murdered! Si and Elmer finally cornered the stranger and attempted to arrest him, only to have the suspected criminal lock them in the bank vault and run for his train...