After the Grail Quest, Launcelot, who was never really known for his short-term memory, forgets the promise he made to live a good Christian life and becomes Gwenyvere's lover all over again.
To avoid scandal, Launcelot champions the causes of many different women. But that only causes Gwenyvere to be jealous and exile him from the court.
At Sir Bors' advice, Launcelot doesn't leave the kingdom, but takes shelter nearby with a one-time knight-turned-hermit named Sir Brascias.
To throw everyone off the scent, Gwenyvere hosts a dinner for some of Arthur's knights, which is meant to dispel rumors of her favoritism for Launcelot.
At the dinner, a kinsman of Lamerok, Sir Pyonell, carrying the old grudge about Lamerok's death at Gawain's hands, attempts to poison Gawain with an apple but misses and poisons Sir Patryse instead. Whoops.
Adding to the drama, Sir Patryse's cousin, Sir Mador de la Porte, accuses the queen of the poisoning and none of Arthur's knights will defend her, because they fear being accused of the treachery, too.
At Arthur and Gwenyvere's request, Sir Bors agrees to fight as Gwenyvere's champion in the upcoming trial unless another, better knight, offers to take his place.
Tipped off by Sir Bors, Launcelot arrives just in the nick of time and (in disguise) defeats Mador, then reveals his identity and explains that he will always defend the Queen because of the great kindness she showed him at his knighting.
Meanwhile, the sorceress Nyneve reveals Sir Pynell as the poisoner and Sir Patryse's tomb bears the truth, as well as testimony to the Queen's innocence in his death.
Arthur declares – what else? – a joust and tournament at Camelot, but Launcelot, still recovering from his fight with Mador, declines to attend until Gwenyvere tells him off.
Before the tournament, Launcelot lodges with a baron named Sir Barnard, whose daughter falls in love with the fine knight. No surprise there.
Launcelot decides to carry the shield of Sir Barnard's son as a disguise, and to wear the favor of his daughter, Elayne, the Fair Maiden of Ascolat.
Launcelot and Barnard's son Sir Lavayne take the side of the kings of Northumberland and North Wales in the fight against Arthur, and Launcelot wins the prize.
He then retreats to the hermitage of Bawdwyn of Britain to recover from his wounds, which are pretty nasty.
In search of the "White Knight with the Red Sleeve," Gawain reveals Launcelot's identity to Sir Barnard and his daughter when the young lady produces the knight's real shield.
Gawain tells Arthur's court that the mysterious knight was Launcelot, and that there appears to be great love between him and the Maiden of Ascolat. Gwenyvere is quite jealous.
Elayne travels to Camelot to find Launcelot and, once brought to the hermitage by Lavayne, spends all her time caring for him as he continues to heal.
Sir Bors finds Sir Launcelot and tells him of Gwenyvere's anger. He also laments Launcelot's refusal to marry Elayne, whom he believes would be a very suitable wife. So many women, so little time, Lance.
Bors and Lavayne mount and arm Launcelot because they want to see if he's ready for a Halloween tournament; in the process, his wounds re-open, and painfully so. Needless to say, he won't be jousting in this go-around.
Bors returns after the tournament to find Launcelot healed, and they ride together with Elayne and Lavayne to Sir Barnard's.
Elayne asks Launcelot to marry her or be her lover, warning that she'll die if he refuses. He refuses anyway out of loyalty to Gwenyvere, then returns to court.
Predictably, Elayne does die because she loves Launcelot so darn much. Her father promises to send her in a funeral barge down the river to Camelot with a letter telling how she died.
When Arthur and Gwenyvere discover it, Gwenyvere rebukes Launcelot but Arthur gives a speech about how a knight who is bound in love loses himself.
Arthur declares a Christmas joust, for which Launcelot promises to wear Gwenyvere's favor and let his identity be known, for once.
When resting by a little well, Launcelot gets wounded by one of those stray arrows that keep flying around. This one was shot by a lady-hunter. He enters the tournament anyway and, with Sir Gareth in disguise, wins great honor against Arthur's nephews.
May arrives. The narrator celebrates spring as the season of love and laments the lack of steady lovers nowadays. There are lovers, sure, but they're anything but steady.