Sergeant Preston is summoned to the office of inspector Conrad to be informed that three men have robbed the bank in Selkirk. Two of them, Luke Derben and Jed Hayward, are wanted for a long list of crimes but the third one is just a young boy of sixteen or seventeen unknown to the police but may also be deadly and dangerous. Sergeant Preston is sure to face plenty of peril when he goes in search of this strange trio.