In Susan Cooper, the first full-length critical study of its subject, Nina Mikkelsen argues persuasively that Cooper's books "have much to tell us about the human condition, about children, and about children's literature." Organizing her material chronologically, Mikkelsen commences with a biographical portrait of the writer, tracing influential persons and events from Cooper's growing-up years in a London suburb during World War II to her present-day life in New England.

Individual chapters then focus on The Dark Is Rising sequence, including its English- and Welsh-set volumes and the response from its readers; explore the works of the 1980s and 1990s, among them The Boggart and The Boggart and the Monster, centering on a mischievous Scottish spirit and geared to younger children; and assess the form, structure, and vision marking Cooper's writing as a whole.

Special emphasis is given to the role that Celtic myths play in Cooper's narrative patterns, characters, and themes - myths that, Mikkelsen observes, Cooper "borrows; she invents; she reinvents, and the wide web of stories raying out of the main story reflects the many layers of cultural identity the books explore."