The Cockroach King is the third book in the Sorry and Morticum trilogy. While on the moon colony, Sorry receives an urgent call for help from the earth. Their atmosphere is failing, and Sorry is infuriated that he has spent so much of his life trying to save that planet. Young wizard Soriguard believes an atmospherologist who lives in the mind gardens can help. The crew grows more and more curious as to the present state of the dying planet they left six years ago and decide to help. When they return, their spaceship is shot at and they make an emergency landing with the aid of the giant cockroaches, Spinks and Gronk. They quickly realize that the dying atmosphere is not the greatest of their problems. The world has regressed to a form of behavior abolished six hundred years before, and they have long since forgotten how to hold a proper war. Still, it will take the greatest insights of both Sorry and the Cockroach King, and Soriguard remembering something he learned on the moon to solve this problem.