Sol is the month between June and July on the thirteen-month Moon calendar. It's the only time teenagers have to themselves between rigorous scientific training and their ultimate lab assignments in their colony on the Moon. Their families emigrated from Earth to build better lives; but life on the Moon is far from perfect, as Uma learns on the eve of Sol.
Uma meets an Earthen girl who becomes a fast friend, and much more. What Uma doesn't know is that the girl is assigned to infect Uma with a plague that a rogue faction of Earthen scientists hope will wipe out Moon soldiers. Will Uma be the cause of a pandemic? Whom can she trust, and moreover, whom does she love?