The Holy Grail starts as a simple claim in medieval French romance: a vessel used at the Last Supper, later carried to Britain by Joseph of Arimathea. This account traces that claim through its earliest text, Robert de Boron's twelfth-century Joseph d'Arimathie, in which Joseph receives the Grail from a vision of Christ and sends it west with his followers. Later writers expand the story, having Joseph catch Christ's blood in the vessel at the cross and found a line of guardians sworn to protect it. The film follows how these threads fuse with Arthurian legend through the character of Percival, whose quest becomes the template for every Grail romance that follows, and how pre-Christian Celtic folklore may sit underneath the whole tradition. It also separates the Grail legend from the related but distinct cult of the Holy Chalice, showing where the two traditions overlap and where they diverge. The result is a history of a story rather than a hunt for an object: how a twelfth-century invention hardened into a legend still retold today.