An opportunistic Texas gambler and the exiled Creole daughter of an aristocratic family join forces to achieve justice from the society that has ostracized them.

On a train journey, Saki meets Mrs De Ropp, an oppressive aunt and guardian to an unruly brood. Inspired by the meeting, he imagines a tale of repressed children who find solace in their childish wonder, and are saved by their imagination.

After being falsely accused of a payroll heist, The Kid heads for the high country where he joins a gang of outlaws slaughtered during a daylight bank robbery. Hiding out in a local ranch, he falls in love with the rancher's daughter, who tries to rehabilitate the cowboy.

In 1870s America, a peaceful American settler kills his family's murderer which unleashes the fury of a notorious gang leader. His cowardly fellow townspeople then betray him, forcing him to hunt down the outlaws alone.

The plot of Marine Express can be described in two parts. The first part focuses on the people boarding the train and the problems they encounter on it. The second part takes place after the train has stopped at its half-way point, an island that used to be home to an ancient civilization millennia ago and has its fair share of secrets.