After accidentally opening a portal to another world, alien creatures occupy the earth and bring with them a hostile gas that makes oxygen toxic to human beings. The game follows one of the agents from the organization that is responsible for creating portals as a means of transportation on earth. This agent must follow the portal path to find the source of the portal to the alien world in order to shut it down. On her way there, she must survive alien creatures that can kill her as she makes her way from one portal to another.
