Malory reveals that King Mark has a younger brother, Prince Boudwin, whom he’s neglected to mention up to this point. Boudwin exists, Malory insists. He just hasn’t been involved in literally any of the Cornish events of the last three Books because he was busy.
But he’s Mark’s younger brother, smarter, better-looking, way more charismatic. Shortly after the Sessoins pack up and leave, an expeditionary force of Saracens land at Cornwall and try to invade. Boudwin raises a militia and routs them and burns their boats and becomes the hero of the hour, without even telling Mark about it until it’s all over. Everyone’s very impressed.
Afterwards Mark invites him and his wife Anglides (a woman with a name!) and also his infant son Alisander to Tintagil, to visit.
“You could have told me about that invading army,” Mark says to Boudwin, once alone with him and his wife.
“Enh, it was nothing I couldn’t handle, and if I’d waited for the courier to get to you and then for a response, the invaders would have been doing damage that whole time.”
“Thou liest, false traitor!” booms Mark. “Thou art ever about for to win worship from me and put me to dishonor and thou cherishest that I hate! I am jealous of your bravery and great deeds! You make me feel bad about myself!” And Mark pulls out a knife and stabs Boudwin in the chest, twenty or thirty times. Blood everywhere, Boudwin’s wife Anglides screaming, it’s a bad scene.
Sir Tristram, Sir Dinas, and also Sir Fergus (Tristram’s other sidekick whom Malory keeps forgetting about) all feel pretty dreadful about this, but what can you do? Mark’s king, he can stab whoever he wants apparently. The only person to take any kind of action is the lovely Isoud, who bundles Anglides and her infant son Alisander up and gets them on horses and out of Tintagil before Mark decides to kill them too. This is the most proactive thing the lovely Isoud has done in, like, ever.
Mark goes to murder his sister-in-law and nephew, but finds them already gone. I don’t know why Mark waited, since Anglides was there when Boudwin was killed. But now she’s gone and Mark can’t find her anywhere in the castle. He sends for one of his best men, Sir Sadok, who isn’t that great a guy really but Mark’s men are by and large incompetent dolts.
“Sadok,” he says, “go find Anglides and her son and kill them. Or bring them to me. Either way.”
“You got it, boss,” says Sadok.
Sadok rides after Anglides and catches up to her and invites her back to Tintagil.
“Not into getting stabbed,” she says.
“That’s understandable,” Sadok says. “I don’t suppose you’re planning on raising Alisander to avenge his father’s death?”
“Well now I am,” says Anglides. “That’s a great idea!”
Sadok returns to Mark. He lies and claims he murdered Anglides and Alisander both. And thereof King Mark was full glad.
Anglides rides and rides until she gets to Arundel, in Sussex, where she has a castle. There she meets up with her cousin’s husband Bellangere and they all live there in Arundel for years and winters, til Alisander was big and strong and wait, what?
Yeah, Malory is skipping ahead twenty years to tell how Sir Alisander avenges his father’s death. And no, Mark and Tristram and Launcelot and Gawaine and Arthur and Guenever are not going to be twenty years older next time we see them. Malory doesn’t see why we’d have any problem with that.
There’s also a bit here about Alisander inheriting his father’s shirt with all the blood and stab-wounds on it, which is reminiscent of the tale of Sir Ill-Fitting Suit, way back at the start of Book IX, but Malory insists they’re totally different stories and no way has he gotten his timeline muddled, it’s me who has the problem, not him.