From publisher blurb:
A 5th Edition Mini-Dungeon for four to six characters of levels 11-14
A Tale of Two Liches takes place in an underground complex housing an inexhaustible supply of necrotic energy. Before lichdom, Pragnazok devised a way to fuse his essence with a golem, but the fusing would kill him unless he assumed lich form. The process also required tremendous amounts of necrotic energy. Pragnazok located a rift that provided the energy but was thwarted by the presence of a demilich that controlled the source. Seeking to usurp the demilich's control, Pragnazok attempted to wrest control of the power source, but something went wrong. The phylacteries of Pragnazok and the demilich became linked. While the demilich is corporeal, its phylactery cannot be destroyed without destroying Pragnazok’s. Pragnazok is trapped, unwilling to leave his phylactery at the mercy of the demilich.