An excellent read. The reader will not fail to note the many levels of historical parallels characteristic of Piper's work, which were not affected by Kurland's finishing.
Spanning centuries, it outlines the development and eventual contact of races arising on a binary planet system. One, the Thalassans, develops a totalitarian theocracy, and the other, the Hetairans, never develops either a religion or a government, per se. Their entire culture is based on - in the words of a friend I lent it to - "Knowledge... leads to more knowledge. We LIKE that."
-SPOILER ALERT -
When contact is made amicable relations gradually sour and both races come to the same decision and implement it simultaneously.
Piper hid a joke of sorts in the book which requires special knowledge to catch. The principal god of the Thalassans is Vran. The closest English transliteration of the Russian acronym equivalent to the American MAD (Mutually Assured Destruction), is VRAN.