Normally, these realities co-exist peacefully, impinging on each other nary at all. Oh, some people can percieve the alternate realities; they have been called anything from visionaries to lunatics, depending on the culture they came from. But they have always been in the small minority; the great majority of the people in all realities believe that theirs is the only true cosmos, and the rest is simple fiction.
Then there are Vortices.
A Vortex is a place where the fabric of spacetime is, for some reason, particularly weak. It isn't just a location -- it's a particular place at a particular time, where multiple planes impinge on one another. In a Vortex, one or many people can "crossover" into an alternate plane, seeing and interacting with the people there. At one time, Vortices were relatively rare, but recently they have become more and more common. While the theoretical underpinnings of Vortices are still only hazily understood, their effects are quite clear. They are stretches of spacetime where synchronicity becomes the rule, rather than the exception, and where physics become almost "literary" in nature. They generally last until brought to a satisfactory resolution (although not always a happy ending). Once that is achieved, the Vortex closes, and the agents are automatically returned to this universe. (The television series Quantum Leap was based on some of the early theories about how Vortices operate.)
One element of Vortices has gradually become clear: they are occasions where belief affects the universe far more strongly than usual. Experiments have demonstrated that the details of the Vortex that opens tends to depend heavily on what the people near it believe will happen. It has gradually become clear that many of the miracles throughout history have probably been due to well-timed Vortices, interacting with what people want to have happen. And it looks like a sufficiently powerful Vortex can leave after-effects; elements of the crossover can remain permanently. This is why it is important to have agents in the field, making sure that Vortices don't have too many after-effects, and close down solidly; if the participants believe that the event is over, it generally is.
About Fifteen years ago, a particularly large Vortex sucked together people from a variety of places and times, nearly bringing about a disaster of galactic proportions. It was that day that began the experiences of the first modern Vortex Mechanics, and would eventually lead to the creation of the ILF.
The Interactive Literature Foundation is a pleasant, safe-looking cover for one of the most important missions running today: the preservation of linear, rational spacetime. Over the years, it has developed a modus operandi that has served it well. The expert Vortex Mechanics at ILF Central (in a secret complex near Washington, DC), using advanced mathematical models, calculate the time and location of the next Vortex. Agents are sent in, under the guise of "gaming"; this cover story enables them to explain almost any sort of bizarre occurances to the locals. (It is remarkable what people will accept as a "costume" -- most people are easily fooled into believing that the world is, in fact, rational, even mundane.) These agents enter the Vortex, attempting to blend into the situation as best they can, and try to assemble a fair conclusion that will bring the Vortex to an end. The ILF's record has generally been good, and has improved with experience; time has taught the Foundation much, and they have been steadily training new field agents.
You are a Field Agent of the Foundation, sent in to work on an especially large Vortex, which has drawn in a number of sub-Vortices. Despite the hard work of the Foundation, all the signs are that the Vortices are, for some reason, gradually accelerating. It was only a few years ago that Vortices of this scale were fairly rare, happening perhaps once a year. Now they can be counted upon twice a year, and the number of small Vortex Events is growing -- it sometimes seems like one happens almost every week. This one is expected to be huge, so they've called on every Vortex Mechanic they could lay hands on, even drafting a few new ones for the occasion. It looks to be a lot of work for everyone. The Vortex is currently projected to peak late Saturday night, at about 1:30am, during Any Port in a Storm. It looks like some sort of massive Vortex will break open at that point; to warn everyone, the ILF has arranged to have one of its own people acting as DJ for the party. She will play REM's It's the End of the World as We Know It to cue everyone when it looks like the Vortex is about to break open.
Making all of this more complex is the apparent presence of one or more Chaos Vortices. A Vortex of Chaos is a sort of semi-permanent Vortex; it attaches itself to a place, thing, or person, and attracts Vortices to itself. While you haven't been told explicitly about a Chaos Vortex being here, the effects are readily apparent -- greatly heightened synchronicity, conflicts occuring on a large and complex scale, and general confusion.
That confusion manifests itself in all of the groups that have converged upon this Vortex. It's enough work dealing with a Vortex on its own; this time, though, intelligence indicates a number of chaotic factors added in: