At the feast of Pentecost, a damsel comes and asks that Sir Launcelot come with her. He goes and meets Galahad, his son, makes him a knight, and invites him to court. Launcelot rides to court ahead. Magic writing appears on the Sege Perilous — the seat at the Round Table which no man has yet been worthy enough to fill — revealing that the seat will be filled today.
Then Arthur and his court hear of a sword in a floating stone, and on the pommel a legend claiming that this sword belongs to the best knight in the world. The king suggests that the sword belongs to Launcelot, but Launcelot says no and refuses to try to draw it out. The sword has a curse, he says: the man who tries to pull it out and fails will get a grievous wound from it later. Arthur orders Gawain to try and he does so willingly, accepting the curse because it was at Arthur's command. Then Percival tries it "to beare Sir Gawayne felyship" in the curse. Galahad arrives, takes the Sege Perilous, and acquires the sword.
Then the Grail Quest begins. Because he knows he will never see all his knights together again, Arthur orders a tournament at Camelot. Galahad, riding without any shield, proves himself brilliantly. At the feast afterward, the Grail appears, hidden under drapes, and feeds all the hall. Most of Arthur's knights vow to go on the Grail Quest, and to the sorrow of Arthur and his queen, they depart.