Rimon Farris, a rich Sime farmer's son, has a golden future: all he has to do is marry his childhood sweetheart, Kadi, and he's set for life. But Kadi matures into a Gen, as one-third of the human children do, randomly; and suddenly is considered no more than a food animal, a thing to be killed and harvested.

The couple refuse to accept their fate, and flee to a strange hybrid community. There they set in motion the greatest social engineering experiment in human history. If it succeeds, Simes will finally be able to live peacefully in a symbiotic relationship with the Gens. But if it fails, all will be lost...