Every year, the Changed generously allow a hand-picked group of human children to come up from Babelion and be tested alongside their own young. But the Changed know, as the humans do not, that it's a sham. The humans will always fail. They don't have the right genetic makeup and the years of intensive training it takes to mesh properly with the computer system where the test takes place. Their best will never be enough. It's a subtle way of teaching them their place.

Then, one year, Arsen shows up: strong, smart, wildly charismatic, and not at all convinced of the superiority of the Changed. Still, he's nothing the system can't cope with -- until he hooks up with Della, Changed born and bred, but every bit as rebellious as Arsen. She, too, doubts that the serenely self-absorbed Changed have all the answers.

What starts between Arsen and Della will tip their whole universe on its side, and start it rolling downhill...