For 600 years, a colony of humans have lived on Gamma Draconis III. It's a planet that has various humanoid species and clans, where a planetary year lasts 60 Earth years, so each person experiences but one long turn of the seaons in a lifetime. Constrained by League of All Worlds precepts not to use or introduce more sophisticated technologies to the planet's inhabitants than they already have, the "Alterrans" have slowly devolved -- forgetting the use of space ships and shrinking in population, although some have developed basic telepathy skills. Agat, one of the "farborns" as the planet's indigenous peoples call them, falls in love with Rolery, an independent-minded female of the Tevar, who marries him even though they cannot reproduce. The beastly and primitive Gaal are invading from the north, in front of the creeping Winter season, and instead of merely scavenging they have formed a united army, so the question is whether the historically distrustful Tevar, Pernmek, and Allakskat can form an alliance with the "farborn" Alterrans to stop or divert the Gaal. This early LeGuin (1966) is more unified and satisfying than _Rocannon's World_ (there is even a passing mention of Rocannon in this book), but still fairly basic.
The review of this Book prepared by David Loftus