In a central part of Turin Cathedral is an elaborate, baroque shrine housing one of the Catholic Church’s most precious and controversial artifacts: a 15-foot-long piece of cloth known as the Turin Shroud, whose surface bears, in faint shades of brown, the unmistakable image of a man. For its dedicated believers, known as “Shroudies,” this image is that of Jesus Christ himself, burnt onto the cloth upon his miraculous resurrection from the dead. But the debate over the shroud's origins has raged furiously since its first documented appearance in Lirey, France, in the 1350s. Is it the authentic burial shroud of Jesus Christ, or just a brilliant medieval fake? In 1988, three of the world’s foremost carbon-dating labs announced in agreement that the Shroud could be dated only as far back as the 13th or 14th century. Then in the summer of 2002, a team of textile restorers was invited to Turin to undertake an unprecedented renovation of the shroud, which called for the removal of the shroud's backing cloth and all of its medieval patches. The results were staggering...