In the wake of an environmental catastrophe, January, once a principal in London's Royal Ballet, has become a refugee in Tharsis, the terraformed colony on Mars. There, January's life is dictated by his status as an Earthstronger-a person whose body is not adjusted to lower gravity and so poses a danger to those born on, or naturalized to, Mars. January's job choices, housing, and even transportation are dictated by this second-class status, and now...