A stirring drama spiced with mystery and adventure centered around the crushing of a desperate gang of Train Bandits by the U. S. Marines.

Veteran serial director George B. Seitz keeps things perpetually on the move in The Great Mail Robbery. Theodore von Eltz stars as Marine lieutenant Donald Macready, assigned by his commanding officer to squelch a train-robbery gang. Going undercover, Macready infiltrates the gang and monitors their every move.