Enlightenment professor Nicholas Caritat is sent to find the best possible world. On his mission, he encounters the Militarian Pessimists, and their opposition, the revolutionary Optimists. The Optimists are having a hard time of it against the Pessimists, and they send Caritat in disguise (as Professor Pangloss) to Utilitaria, a country where everything runs efficiently and smoothly but which is ultimately as oppressive as Militaria. Caritat then travels to Communitaria and Libertaria, where he encounters the metaphorical extremes of contemporary governments.