From the rulebook:
Guardians of the Gates
Building dungeons, taking over land and feeding off human hope, the Cima have created a realm of desolation and despair. Some have chosen to fight this new danger by becoming "Gate Guardians"--those that protect the innocent from becoming ensnared in the Cima's dungeons. Ark and Ivy, two young Cima fighers, are new Gate Guardian recuits. While traveling with their mentor, Jester, and 14 others bound for a new frontier, the train is sucked without warning into a Cima Gate and everyone on the train becomes separated in the cavernous dungeons below. Ark and Ivy's first task is to find, protect and add these people to their fighting party as they are plunged into a mysterious and frightening new world.