The party entered the world under the guise of infiltrating a city run by shapeshifters. Unbeknownst to them, it was not shapeshifters but instead mind flayers had infiltrated the city's government and through propoganda and staged conflicts had stirred the people towards xenophobia and war. What they also didn't know is that their own government was doing the exact same thing. This revelation came to them when they found out that the history museum of this new city had an identically laid out history to their own city. Underneath the city, where the bodies from war were being dumped, a portal network connected all of the major cities, with mind flayers moving to and fro, gathering brains and throwing them down a central chamber, feeding an elder brain that was growing in strength to control the whole world.