Over the years, scholars have labored to show that C. S. Lewis's famed Chronicles of Narnia have an underlying symbolic coherence, pointing to such possible unifying themes as the seven sacraments, the seven deadly sins, and the seven books of Spenser's Faerie Queene. None of these explanations has won general acceptance and the nature of Narnia's symbolism has remained a puzzle.

Michael Ward has finally solved the mystery. In Planet Narnia, he argues convincingly that medieval cosmology, a subject which fascinated Lewis throughout his life, provides the imaginative key to the seven novels. Drawing on the whole range of Lewis's writings (including previously unpublished drafts of the Chronicles), Ward shows that the Narnia stories were designed to express the characteristics of the seven medieval planets - the Sun, the Moon, Mars, Mercury, Venus, Jupiter and Saturn - planets which Lewis described as "spiritual symbols of permanent value" and "especially worthwhile in our own generation." Using these seven symbols, Lewis secretly constructed the Chronicles so that the story-line in each book, countless points of ornamental detail, and, most important, the portrayal of the Christ-figure of Aslan, all serve to communicate the governing planetary personality. For instance, in The Voyage of the "Dawn Treader," the sun is the prevailing planetary spirit: magical water turns things to gold, the solar metal; Aslan is seen flying in a sunbeam; and the sun's rising place is actually identified as the destination of the plot: "the very eastern end of the world."

Planet Narnia is a ground-breaking study that will provoke a major reassessment not only of the Chronicles, but of Lewis's whole literary and theological outlook, revealing him to be a much subtler writer and thinker than has previously been recognized.