Doctor Sax (Faust Part Three) is a novel by Jack Kerouac. The third book of Kerouac's autobiographical series, the story unfolds in the author's hometown of Lowell, Massachusetts. It follows the dark and mystical adventures of the protagonist Jack Duluoz, Kerouac's alter ego, as he navigates a realm of fantasy peopled by the enigmatic figure of Doctor Sax and other characters.