Fifteen-year-old Charles Wallace Murry, whom readers first met in A Wrinkle in Time, has a little task he must accomplish. In 24 hours, a mad dictator will destroy the universe by declaring nuclear war--unless Charles Wallace can go back in time to change one of the many Might-Have-Beens in history. In a suspenseful journey through time, this extraordinary young man psychically enters four different people from other eras. As he perceives through their eyes "what might have been," he begins to comprehend the cosmic significance and consequences of every living creature's actions. As he witnesses first-hand the transformation of civilization from peaceful to warring times, his very existence is threatened, but the alternative is far worse.

The Murry family, also appearing in A Wind in the Door and Many Waters, acts as a carrier of Madeleine L'Engle's unique message about human responsibility for the world. Themes of good versus evil, time and space travel, and the invincibility of the human spirit predominate. Even while she entertains, L'Engle kindles the intellect, inspiring young people to ask questions of the world, and learn by challenging.