Is sex an enemy that must be subdued before spiritual practice can happen, or is it a powerful creative force and a vehicle of enlightenment? There may be no completely satisfying answer—though the question has engendered discussion for centuries. David Guy's contribution takes the form of a personal exploration of the place of sex in his own life and meditation practice, as well as in the lives and work of figures he has come to regard as pioneers on the boundaries of sex and spirituality: Walt Whitman, D. H. Lawrence, Alan Watts, and the erotic writer Marco Vassi among them. It also includes accounts of his pilgrimages to contemporary theorists, activists, and sex workers. From poets to prostitutes, everyone has something to say, even though the reconciliation of sex and spirituality may always remain something of a paradox—as expressed in the Zen koan from which the title is taken: "Why is it that the most clear-eyed monk cannot sever the red thread of passion between his legs?" David Guy's answer is this honest and compelling exploration of the nature of desire.