Glory Season - David Brin

A woman faces danger on the high seas of another planet—and a mystery that will change her world—in this adventure by the bestselling author of Startide Rising.
On Planet Stratos, clans of genetically identical females dominate society. Natural conceptions are permitted, but only in summertime. Girls born this way—known for their despised uniqueness as 'vars'—must leave their clan homes to pursue their own distinct and hazardous fortunes in this world owned by clones.
That time has come for Maia and her sister, Leie, but as variants, they have limited prospects. Worse, when the sisters do find work on trading vessels, Leie is lost at sea.
And hence, Maia's arduous journey commences, accompanied by rumors that something . . . someone . . . has arrived from across the stars, perhaps ending the isolation of Stratos from the rest of humanity. Who would predict that a lonely var might stumble into a powerful secret? One that will challenge everything Maia knows about her society—and threatens the scientifically-engineered balance that holds it all together.
"One of the most important SF novels of the year." —The Washington Post Book World
"A rousing adventure story . . . brimming with surprises both wonderful and harrowing." —The San Diego Union-Tribune
"Glory Season offers thrills, chills, political intrigue, and other good scientifictional fun, along with yet another round in the battle of the sexes." —Locus
"Brin's prose echoes the influence of Asimov, Frank Herbert, and Aldous Huxley. . . . His world is so painstakingly drawn and is splashed with such radiant and varied hues." —The Christian Science Monitor