Complex sentence: Upon arriving, they find themselves in the midst of a group of Imperial Order advanced scouts who have captured a girl named Jillian, part of a people called the "Dream Casters".
Split into simpler sentences: Upon arriving, they find themselves in the midst of a group of Imperial Order advanced scouts that have captured some of the people there. The reader is introduced to a girl named Jillian and a people called the "Dream Casters".