The human gene pool was falling apart under environmental assault. The solution - simplify it, making it redundant and self-correcting. When the planet is clean again, change it back. Meanwhile, a rudimentary civilization can go on. But after two thousand years, there are still intolerable mutation rates. Achibol the Sorcerer, dilapidated cyborg troubleshooter, is repairing them one by one, but someone-or something-doesn't want him to succeed. The urchin Benadek, Achibol's apprentice, only wants good food and a warm place to sleep. But nothing is ever what it seems, including Benadek. And nothing human is ever...simple.