This 32-page book begins with a two-page introduction. According to the adventure background provided, the plot involves a fortress that became buried in the earth ages ago, and became known as the Sunless Citadel. In the citadel's core grows the terrible Gulthias Tree, shepherded by the twisted druid, Belak the Outcast. The Tree spawns magical life giving (and life stealing) fruit, as well as evil creatures known as twig blights. The adventure starts with player characters hearing rumors about the citadel while staying in the nearby small town of Oakhurst. The majority of the adventure then focuses on the characters exploring the citadel and encountering the malign creatures that have taken up residence within, such as kobolds and goblins. The characters eventually come upon the Twilight Grove and its blighted foliage, where they find the Gulthias Tree and encounter the druid Belak. He explains that the tree grew from a yet-green wooden stake that had been used to kill a vampire on that very spot, and the tree accepts humanoids bound to its bole as "supplicants", making the victims completely subservient to its will. A three-page appendix at the back of the book features statistics for all of the creatures encountered in the adventure, as well as three new magic items and the twig blights.