World Gates is part of the Dark Moons on Chimera series. It is actually Book 5 and relates how Terry and Tiffany of Earth are ripped from their life and thrust into the politics of a world they don't know anything about. Mhel'Sargonus must step in and help them but they are also asked to assist a Princess in her quest to find her brother and free her sister from a wicked King and the Guild.