Emperor Lucius of Rome sends messengers to Arthur's court demanding tribute. Though Arthur is furious, he controls himself and takes council with his knights. Sir Cador is delighted with the possibility of honorable war; the King of Wales vows vengeance on the Viscount of Rome, who once treated him shamefully; the young Launcelot du Lake eagerly offers his aid; and the remaining knights also pledge their full support. Arthur gives the envoys of Rome their answer and they leave. They warn Lucius of Arthur's might, but Lucius attacks nevertheless, supported by giants and Saracens. He takes the lands Arthur won from King Claudas and moves toward Normandy. Arthur leaves his kingdom in the hands of two noblemen and Guinevere, and, though his wife swoons from grief, prepares to embark. If he dies, Constantine, Cador's son, is to succeed him.
On his ship, Arthur dreams of a battle between a dragon and a huge bear. According to his dream interpreter, the dragon represents Arthur himself; the bear is either some tyrant or a giant he will destroy. As soon as he lands at Normandy he hears of a giant who torments the land, murders women and children, and has recently stolen a duchess, wife to Arthur's cousin. Arthur calls Kay and Bedivere and tells them to arm themselves; they will go with him on a pilgrimage to St. Michael's Mount, "where mervayles are shewed."
They ride through a beautiful countryside full of birds, then alight. Arthur says he will seek the "saint" alone. He finds the grave of the duchess, beside it an old woman who warns him that the giant has no respect for treaties. He will accept nothing from Arthur but Guinevere. Arthur fights the giant, kills him, and jokes more with Bedivere and Kay on this "saint" he has found. He gives away the giant's treasure, attributes the victory to God, and moves on.
