After the 1860s Wild West, a group of misfit settlers including an ex-doctor Phil Taylor (Lewis), a prostitute Belle (Ellen Greene), and homosexual bookseller Julian (John C. McGinley) decide they cannot live in their current situation in the west so they hire a grizzled alcoholic wagon master by the name of James Harlow (Candy) to take them on a journey back to their hometowns in the East.
Melanie Ballard (Natasha Henstridge) is a hard nosed police chief in the year 2025. She and a police snatch squad are sent to Mars to apprehend a dangerous criminal James Williams (Ice Cube). Mars has been occupied by humans for some time and they have set up mining facilities. The mining activities on Mars have unleashed the spirits of alien beings who gradually possess the bodies of the workers. It soon turns out that catching the dangerous fugitive takes a back seat as the alien spirits begin to rid their planet of the 'invaders'.