In Spain, a band of gypsies poach the deer in a neighboring estate. The gypsy chief, Tser (Harold Truesdale), is murdered in cold blood, and the estate owner Winston Graham (Jack Holt) is blamed. The chief's daughter Mona (Dorothy Revier) is an expert knife-thrower and sets out to avenge her father.
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.
"The Stranger," an outcast who works in a saloon frequented by Peggy Bowlin, a poor girl suffering through hard times. She finds romance with Larry Darrant and her life begins to improve. They make plans to wed and leave England, but when a convict assaults Peggy, Larry gets involved and accidentally kills him. The Stranger is arrested for the murder, but he refuses to declare his innocence because he doesn't want to destroy Peggy's happiness.
Betty, a blind girl, is the sole "witness" to the murder of a mine owner and whose mistaken testimony convicts Sid Allen her own benefactor. Years later, the adult Betty returns to the mining town, her sight restored. Fearing that she may remember the truth, the real murderer, "Bull" Snide has the girl kidnapped.
Refusing to marry her stepmother's choice, Gail Prim leaves her life of luxury, after cutting her hair, dressing in her butler's clothes and stealing money and jewels from her father's safe. Spending the night in a barn, she introduces herself to the thieves already there as the Oskaloosa Kid, a wanted criminal, and barely escapes their struggle to get her loot. Meanwhile, the real Oskaloosa Kid kills Reginald Paynter and throws Nettie Penning, whom Reginald was trying to seduce, onto the highway.