The fact that no consistent ‘Grail story’ emerges from the romances is frustrating, and has undoubtedly contributed to the number of speculative theories about its origin. However a basic story outline would be something like the following:
A mysterious vessel or object which sustains life and/or provides sustenance is guarded in a castle which is difficult to find. The owner of the castle is either lame or sick and often (but not always) the surrounding land is barren. The owner can be restored only if a knight finds the castle and, after witnessing a mysterious procession, asks a certain question. If he fails in this task, everything will remain as before and the search must begin again. After wanderings and adventures (many of which relate to events which the young hero failed to understand the first time), the knight returns to the castle and asks the question which cures the king and restores the land. The hero knight succeeds the wounded king (usually called the Fisher King) as guardian of the castle and its contents.
Five knights search for the Grail. Perceval (also called Peredur and Perlesvaus) begins as a gauche boy unaware of his connections with the guardians of the Grail. He fails to ask whom the Grail serves when he first observes the Grail procession. He is reproached for this failing by a loathly damsel figure, and sets out again in despair. After many adventures he meets a hermit and finally accepts his knightly role. He returns to the castle of the wounded king, asks the proper question and takes over the role of Grail king. The suave sophistication of Gawain is a perfect foil for Perceval, but his character is also refined by the Grail search. The two present a contrast between more earthly (Gawain) and more spiritual (Perceval) aspects of chivalry, and many romances alternate descriptions of their adventures. Both visit the Grail castle and fail to ask the correct question and both have a chance to make amends. Sir Bors accompanies Perceval and Gawain on their journey and is the third knight to see the Holy Grail. He is also the one who returns to Arthur’s court to recount the events of the Grail adventure. As the best of Arthur’s knights, it should really be Lancelot who finds the Grail, but as the Grail quest became more spiritual, Lancelot’s adultery with the queen became a problem. Lancelot achieves only a partial vision of the Grail, although it does cure him of madness. Later romance tradition introduced the perfect Grail knight, Galahad, the son of Lancelot and the Grail maiden, daughter of the Fisher King. Galahad is the perfect knight. He occupies the Siege Perilous, the seat at the Round Table intended for the man who will achieve the Grail quest, and his experience of the Grail transforms him completely.