Shora is a world without land. The humans who colonized it chose to reshape themselves, instead of terraforming the planet. Sharers, as the descendents of the colonists call themselves, strive to live in balance with each other and their world. Although they have incredibly advanced biological science, they try to change as little as possible about the natural ecology of Shora, even though it means losing friends and loved ones to vast monsters that roam the ocean. Their highest goal is to strengthen the ecological and social web that ties each creature to another. But they share their solar system with Valedon, a feudal, warlike world. And Valedon wants to expand its hold. Can the pacifists of Shora find a way to understand, and be understood by, their invaders?
I've seen other reviews that decry this book as gender-essentialist lesbian separatism, and I have to disagree. The Sharers are all female, and they are, as a group, very wise. But the book doesn't seem to present being wise as the natural extention of being an all-female society. The original colonists created a society that prizes consensus and pacifism, and those are the priorities they passed on to their descendents. There are many Sharers who are not wise in the least, who are hot-headed, blood-thirsty, or narrow-minded. The Valedon soldiers are male and female, and their chief torturer is a woman. And it's not like men are left out of the book--a male Valedon first learns from a wise (male) seer, then becomes a Sharer. We spend a large portion of the book inside his head, and much of the latter half inside another man's.
I really enjoyed reading the Sharers' struggles. They're incredibly inspirational, and I loved their society (even though I'd hate to live on their world). They refuse to do anything that might harm the Valedons (prefering civil disobedience), but the Valedons only value strength. It's fascinating conflict, but the resolution felt like a cop-out: the Valedons accidentally become convinced that the Sharers have created a time-bomb plague, that could wipe out the Valedons if ever the Sharers are wiped out themselves, and so they decide to leave the Sharers in peace.
That aside, the societies Slonczewski create are engrossingly unique, and the conflict between them made me very tense and anxious.