Spoiler Warning: The movie is set in the mid 22nd century. The planet Mars has been terraformed, allowing Humans to walk on the surface without having to wear pressure suits. The story concerns a police officer, Melanie Ballard (Natasha Henstridge) who is leading a small team to pick up and transport a prisoner named Desolation Williams (Ice Cube). Arriving at the remote mining town where Williams is being held, Ballard finds virtually all of the people missing. On investigating she discovers that the miners found an underground doorway which had been created by an ancient Martian civilization. When the door was opened it released "ghosts", disembodied spirits who possessed the miners.

Violence ensues, as the now possessed miners commit acts of death and destruction, as well as self-mutilation.

Ballard must fight off the attacking miners, escape the town, and if possible destroy the ghosts. Unfortunately all these tasks are complicated by the fact that killing a possessed human merely releases the Martian spirit, which immediately possesses another human.