The basic premise is fairly simple. The Tau Ceti star system is home to two twin planets, Urras and Anarres. Urras is a verdant, hospitable world that has been inhabited by humanoid life for millennia. Anarres, on the other hand, is a sparsely populated desert world that was settled two hundred years ago by revolutionary anarchists. Aside from a single freighter that periodically makes the trip, the two worlds — archist Urras and anarchist Anarres — are completely isolated from each other. The story starts with the first person traveling from Anarres to Urras since the revolution that lead to the settlement of Anarres.