Locked away from sight in Turin Cathedral lies a 14ft long piece of linen. Scorched, patched and yellowed with age, it bears the faint image of a crucified man. Is it the work of a 14th-century artist, or is it the miracle of miracles - a true image of Jesus of Nazareth? To help answer that question, the Holy Shroud of Turin has been tested by the most advanced science known to man.