The Lost Prophecies (Medieval Murderers, 4)

575 AD: A baby is washed up on the Irish coast and is taken to the nearest abbey. He grows up to become a scholar and a monk, but, in early adulthood, he appears to have become possessed, scribbling endless strange verses in Latin. When the Abbott tries to have him drowned, he disappears. Later, his scribblings turn up as the Book of Bran, his writings translated as portents of the future. Violence and untimely death befall all who come into the orbit of this mysterious book.