An elderly gangster just released from prison plans one last job, and gathers a small crew to do the job, but the plan goes sour when one of the crew betrays the details of the operation to a rival gangster.

A turn of the century wild west show struggling to make a living in Mexico comes into the possession of a tiny prehistoric horse. This leads to an expedition to the Forbidden Valley where they discover living dinosaurs. They capture one and take it back to be put on display, leading to inevitable mayhem.