A retired hunter of alien zoo specimens, William Blackhorse Singer, the last Navajo on a future Earth, has come to what he sees as the end of his life. The World Government calls upon him for aid in protecting an alien diplomat from a powerful and hostile member of his own species. Knowing both the importance of the task and his inability to handle it on his own, Singer goes to confront his greatest conquest with a strange bargain. A shape-shifting alien, the last of his species, sits in a special cage at an institute dedicated to the study of extraterrestrial beings. Most frequently he projects the aspect of a one-eyed catlike creature, but he can appear as almost anything.