Taithmarin is one of the worlds that is no longer connected to Athare. When it was originally created it was meant to be a relatively normal world and the fae created the first inhabitants, who had magic. However the magic here evolved faster than anyone expected, as also happened with two of the earlier worlds, but it evolved in a different way. Instead of trapping the fae it decided that they were unwanted and did everything it could to get rid of them. Once this had happened the magic took control of the door they left behind.
The door gathers people who have the ability to use magic, including humans from Earth, and its choices aren't dependent on any other criteria, so there are people who don't fit in. Unfortunately most of these people are humans, which is understandable as magic isn't a part of every day life, and they have their own areas in the towns that they end up in where they don't have to deal with the magical races. They are the minority in the world and often feel they are being mistreated, even though they aren't. Often they are just ignored by the other races in the same way that they ignore the races they don't believe should exist.
Other races that are gathered include the Nox Gadael, the Stormkin, the Caelestis Eira (Celestial Snow people), and the Alati Felis. All of these races have some form of magic, although they don't all know that they have it. In all there are fifteen races living on Taithmarin during Joel and Zoe's time there, although there are several that no longer exist on their home worlds and the door will have to begin searching for other races.