Janna's world was colonized long ago by Earth and then left on its own for centuries. When "offworlders" return, their superior technology upsets the balance of a developing civilization.

Mission Child follows the journeys of Janna after she and her young partner escape marauders who attack their hometown. The girl, fast becoming mature beyond her years, sets off across the planet on an odyssey of adventure, poverty, hard work, war, famine, and rebirth. Janna uses her meager skills to eke out a living in a changing world; she gains and loses a husband, a child, friends, jobs, and more.

McHugh weaves together anthropology, sociology, psychology, and gender relations in this wondrous journey. Janna assumes the guise of a boy for protection, but eventually becomes "Jan" to herself as well as others. Reminiscent of Ursula K. Le Guin's insightful works set in the Hainish universe, Mission Child will doubtless be nominated for a Tiptree Award for its exploration of Janna's gender identity.