The Infinity Files is based around the notion of alternate Earths, Earths where the impossible is possible. (More, the impossible is a part of everyday life.) These other Earths are therefore alternate realities, and (within Infinity, Inc.) the term Reality refers to one of these other worlds.
The main campaign setting is our world, pretty much exactly (save for the existence of portals). Its history, geography, levels of development, and so forth are all identical to the world we know.
There are (potentially) hundreds or thousands of Realities, some of which closely resemble our Earth, and others which are highly variant. (Such as Orrey Earth, where the solar system is literally spheres on wires, which orbit the sun on massive gears the size of the moon.) No one has made any concerted effort to survey the many alternate Realities, and such an endeavor may actually be impossible (as a practical matter).
Depending on the campaign, one, ten, or a score of different Realities may appear on Earth. In game terms, each is defined by its Development Ratings (Tech, Social, Magic, Spirit, Psi) and further distinguished by its Setting Rules. Setting Rules are a core part of setting design in Infinity, and in The Infinity Files each Reality has its own set. For the purposes of this campaign, they’re known as Reality Laws, as they define the laws that the alien Reality operates under.
When a portal first opens, the alien Reality begins to leak into our own, allowing the alien Development Ratings and Reality Laws to hold sway, creating a place where the impossible is now possible. Spontaneous alien phenomena begin to occur (such as flashes of psychic visions, Tarot cards actually foretelling the future, and the like). In Infinity, Inc. parlance, this is a “Threat-1” incursion.
Threat-2 incursions allow artifacts from an alien world to function. (Examples include magic swords, religious relics of dark gods, or psychic imprints.) During a Threat-3 event, people from our world begin thinking like people from the other Earth, and can begin to learn, make, and use tools from that Reality. Artifacts from alien world can cross into ours during a Threat-4 incursion, and beings from those worlds can cross over during Threat-5 events.
Threat-6 incursions are the most severe. The portal opens wide, allowing a large number of beings from that world to cross over. More, the area being encroached upon begins to change, the buildings, tools, and people of our world converting into buildings, tools, and beings appropriate to the invading Reality. Secondary portals, spun off from the primary portal, begin to move out, spreading the alien area of influence. Leading portal scientists believe that a Threat-6 incursion could quickly become permanent, eventually spreading everywhere, marking the end of our Reality. (There are many secret organizations devoted to bringing about just such an event.)
All known portals are one way, one Reality impinging on another. Infinity, Inc. is primarily concerned with portals that allow alien Realities to affect our own, but portals that allow the opposite do exist. These latter portals are unnoticeable from our end, until they’ve reached the Threat-5 stage (when people from our world can cross over). Such adventures are very different from the norm, and can make a nice change of pace.
[Continued in Part IV.]