L'Engle is concerned with the mythical—and what she sees as the very real— conflict between the forces of good and evil. Unlike the previous books in the series (A Wrinkle in Time and A Wind in the Door], this novel focuses on individual choice as a factor in the war between good and evil. L'Engle examines the personal choices made by the characters with whom Charles Wallace merges to make the point that it is only on the individual level that the real battle for control of the universe takes place.

Although the mysterious Echthroi appear to be working to thwart Charles Wallace and Guadior, the real presence of evil is embodied in the persons he meets during his twenty-four hour journey in time toward the present. The choice of whether to destroy or preserve life, tribe, or family is made by each...