Notice that some of the doors are walled off, separating whatever lies beyond the door from the rest of the Continuum, leaving that unknown place either dead or dying. Each door opens to a world and when, for whatever reason, the world begins to close itself off from the Continuum, a Sealing Team goes out and tries to stop the world from destroying itself.
Earth finds itself in dire straits.
The web of evil magic that infects the Earth snares the Sealing Team sent to rescue the planet. The team loses two of its members down to the last memory of their existence. Adam Al-Aziz, the Guardian, comes to discover what happened to them and to help salvage the Earth. Bound by Continuum rules requiring them to use the strictures and practices of a religion currently in place in the target world, the Team chooses Wicca for its Earth operations, because Wicca allows the use of magic. Adam's roommate, Rob, never expected to help save the Earth, especially in the company of such a being as Adam.