After following the signal from a magical key to a remote estate in Ustalav, the Pathfinder Society made contact with a truly unusual being as well as the mysterious Ardis Scholars. Yet the scholars are now in dire straits—thanks to the machinations of a long-time foe of the Society, most of their members have been imprisoned in a flying castle tucked away in the Shadow Plane! It's up to a group of veteran Pathfinder agents to mount a daring rescue. But those agents must tread carefully, or the bizarre castle, infused with nightmares and otherworldly technology, will become their eternal prison.