The only version of this poem survives in the British Library Manuscript Harley 2252. The poem is 3,969 lines long and can be dated between 1460 and 1480. The romance was written in an East Midland dialect by two different scribes using eight-line stanzas of four-stress lines. Another stylistic feature that is used quite often is alliteration.
The plot of the poem can be divided into two parts. In the first a tournament is held at Winchester by King Arthur. During this tournament the Maid of Ascolat falls in love with Sir Lancelot. Though he does not return her feelings he wears her sleeve at the tournament, making Gawayn as well as Queen Guenevere believe that he is her lover. The queen rebukes him and sends Lancelot away. This is a big problem for her because shortly afterwards the queen is accused of having poisoned a knight and because she has no champion to defend her she is about to be burned. At the last moment though, Lancelet appears and defeats his opponent in single combat which proves the innocence of Guenevere.
The second part of the poem begins with an ambush of the lovers Lancelot and Guenevere by Sir Aggrawayne and his men. Lancelot succeeds in surviving the ambush and rescuing the queen, but in the fight two of Gawain's brothers are killed. Lancelot flees, pursued by Gawain, which results in a siege of Lancelot's castle in northern France. This war can only be stopped by the news that Mordred has seized the English throne. In the battle that follows Gawain is killed and Arthur and Mordred meet in order to try to make a truce, but an adder appears and a sword is drawn and the fighting goes on. In the end Mordred is killed and Arthur mortally wounded. The King is then brought to Avalon but his tomb is found the next day. Guenevere takes the veil and Lancelot lives the rest of his live as a hermit.
This poem is one of the most tragic Arthurian stories we know. The main influences on the plot come from the three main characters, Lancelot, Guenevere and Gawain. The interaction, misunderstandings and feelings between these characters supply the poem with a vivid driving force culminating in the utterly tragic end.