To save a dying race, sociologist Caleb Faulkner will forfeit his humanity. He has volunteered to join with an alien creature in order to take part in an ambitious breeding program designed to spare the dominant race on the planet Icarus from certain extinction. Dr. Zara Abbott has spent months helping to prepare Caleb for the joining, hiding her feelings for the man who will become the mate to an Icarian female as soon as he receives his symbiotic wings. When the joining proves disastrous, Caleb and his alien symbion can think of only one thing, mating with Zara. After so long preparing to sacrifice Caleb to the Icarians, will she be able to refuse the man who makes her heart take flight.