Episode Duscae has Noctis and friends stuck in a region called, you guessed it, Duscae. The area that you’ll get to explore in the demo is only a fraction of the region, which itself is part of a much larger world that is supposed to be more than 10 times bigger than the Duscae region.
There’s a very good reason as to why you’ll be stuck in the Duscae region in the demo: your car has broken down because of the actions of a “certain blonde guy”, whom we can all assume is Prompto. In order to fix up your car, you’ll have to raise some money to get the mechanic Cindy to do it for you. The methods of acquiring the money needed for repairs is up to you, but the demo’s main quest lies elsewhere.