In the jungles of the Mwangi Expanse, a large group of Pathfinders stands ready to travel beyond a magical gateway whose mysteries stymied a group of the Pathfinder Society's founders. What lies beyond the doorway is also the crux of the plot of an ancient evil fey, the Thorned Monarch. Will the Pathfinders unlock lost fey magic, restore buried secrets from the Society's history, and purge the world of the Monarch's evil, or will they fall before the fey's minions and tricks?