The heroes defeated the Rat King and his minions, and have since moved onto to other adventures. But the Rat King is back, and he seeks revenge! While investigating a ring of slavers, the heroes find themselves delving into the city slums and sewers. Unknown to them, the dungeon is a ruse designed to lure them into the clutches of the Rat King. Faced with too many minions, the heroes are captured and tossed into a dungeon cell, bereft of armor, weapons, and equipment. Can they escape the dungeon, fight their way through a horde of minions, and confront the Rat King again?

Revenge of the Rat King is an adventure intended for four to six 5E characters of 5th level. It is designed as the sequel to Fifth Edition Fantasy #31: Idylls of the Rat King, but can be played on its own without having experienced that adventure.