[4] Gaston Paris gives a much more detailed explanation, in prose, in Histoire littéraire de France, volume 30, pages 223-234 (also in French).
Two knights, Meraugis and Gorvain, travel to a tournament where they meet the beautiful Lidoine, heiress to the kingdom of Cavalon now that her father has died.
Meraugis locates Gawain in the 'city without a name', trapped on an island, held captive by a woman who controls the only boat.
In order to escape, Meraugis feigns defeat to Gawain, and, under cover of darkness, goes into the castle on the island, locks the woman in her room and steals some of her clothes.
However, Lidoine has promised her kingdom to Gorvain for coming to her aid, so Meraugis challenges him to one final duel.