Thousands of years in the future, all the northern hemisphere is buried hundreds of feet deep under the ice and snow of a new Ice Age. At the southern end of a large landmass called Ifrik, two children of the Mahondi people, seven-year-old Mara and her younger brother, Dann, are abducted from their home and family in the middle of the night. Left in the care of a sympathetic Mahondi woman, Mara and Dann are raised as outsiders in a poor rural village. They learn to survive the hardships and dangers of a life threatened as much by an unforgiving climate and menacing animals as by a hostile community of Rock People who wish them ill. Eventually they join the great human migration North, away from the drought that is turning the southern land to dust, and in search of a place with enough water and food to support human life.

Trekking through a barren countryside, Mara and Dann discover different people and places and survive a series of hazardous adventures. They outwit hostile travelers and city dwellers who would kill them for a pittance, and join the increasingly desperate struggle for subsistence in a world transformed by unpreditable climatic change. Captured and enslaved by the Hardon people, they eventually escape and continue North, through the wet heat of the River Towns, only to be captures again by a military commander in the country of Charad. Dann becomes a general in the army, while Mara is recruited as a spy and even abducted for breeding purposes by a rival ethnic group. Traveling across the continent, the siblings enter cities rife with crime , power struggles, and corruption, learning as much about human nature as about how societies function.

Mara's mind is as restless as her feet, and she hungers after knowledge and answers to her questions: Who are my parents? Where do Dann and I come from? Who once lived in these ruined cities we find in Ifrik, and when? And why did they disappear? What will we find up North, and where, exactly, is the North? All the while she dreams of water, trees, and beautiful cities, and of gentle, friendly people. Powerful natural forces, indifferent to human life but essential to its survival, determine the course of Mara and Dann's journey. And Marawith a thirst to learn almost as strong as her thirst for water, and a compassionate, loving nature that survives despite the cruelty of the environment and of human behavioris one of Doris Lessing's most appealing heroines. Filled with shrewd observations and a clear-eyed vision of the human condition, Mara and Dann is imaginative fiction at its best from a master of the genre.