Deciding to be a member of the underground is a momentous decision. It essentially means that you'll be committing yourself permanently to the destruction of the Conspiracy. The underground cannot allow dabblers, they need committed elements.

Though it's very possible that your recruiter may know your name, it's important not to share details about one's identity with other members of the underground. Doing so means that losing one member makes it easier for other members to be captured subsequently. To that extent, codenames are used instead of real names at all times. You need to select one.

So the basics are these. Beings from other places than our world have come to our world. It appears likely that they've been coming over for all of humanity's history, and perhaps longer (who can say?), but that it appears that their influence was limited. As of some point in the twentieth century, probably the latter half, that changed. Humans have always been capable of unexplained powers, but these, too, seem to have become more potent at around the same time as the increase in influence by creatures of the otherworlds.

This also happens to coincide somehow with the appearance of aliens from other stars in our world. Though some speculate that these “aliens” may actually have come from just another of these other “dimensions.”

Often referred to as “proto-dimensions” as these other worlds are thought to be generally more rudimentary than ours. Though some feel that's just our perspective on the subject.