Sir Marhaus sees Tristram coming at him, and steps back.

“Hey there, kid, you’re Melodias’s son Tristram, right?  You’re plainly very brave, which is a shame, since I’m a remarkably badass knight.  I mean, I’ve fought plenty in my day, let me tell you.  You don’t want a piece of this.  Go home, tell them to send an actual knight.”

“O glorious knight,” intones Tristram.  “You surely understand that I cannot do that, for I was made a knight specifically to fight you today.  As the son of a king, and also the son of a queen, and also the nephew of a different king, I promise that I will fight you and in so fighting, save Cornwall from needing to pay taxes to Ireland.

“Truly tax amnesty is the greatest cause for which I could possibly fight!  I am filled with love of my homeland (Cornwall) and pride at having been named a knight!  Also, I was just now named a knight, let me stress again.  I have never jousted before, but I look forward to it.”

“….okay,” says Marhaus.  “Listen, kid, I don’t want to just straight up murder you.  I’m an experienced knight; you have never jousted before today.  So, tell you what.  I’ll spot you three hits.  I have a reputation to maintain, you understand?  I mean, I’m in the Round Table.”

Then they joust.  It looks at first like Marhaus is going to win, but then, Tristram wins!  Didn’t see that coming, did you?  Okay, probably you did.  But here’s something you didn’t expect.  The joust ends with Tristram swinging his sword into Marhaus’s helmeted head, and the sword slicing through the helmet and getting into Marhaus’s skull, and getting stuck in his brainpan.

Tristram tugs on his sword, but can’t get it out from Marhaus’s skull.  Best he can manage is snapping the sword at the hilt, leaving the blade lodged inside Marhaus’s brain.  Marhaus howls and staggers and loses the ability to speak coherently, maybe because of the metal embedded in the language centers of his brain?  He staggers off, throwing away his shield and sword, and makes it back to his ship.

Tristram sees Marhaus leaving, and is like, so did I win?  “Where are you going, sir knight?  Are you running away?  I don’t think that’s allowed!  I know this is my first joust so I might not be completely up on the rules, but I’m under the impression you don’t get to just flee like this.  I mean, I’m pretty sure I wouldn’t run away if I were hurt.  Like, you could cut me up into a bunch of pieces, I’d keep fighting…”

Marhaus babbles incoherently, which Tristram takes to mean he’s won.

“Well all right then,” calls Tristram.  “I’m just going to take your sword and shield that you dropped, okay?  They have better plusses on them than my stuff.”

Marhaus’s crew takes his ship back to Ireland, where Marhaus staggers up to King Anguish and dies.  Anguish isn’t thrilled by this, but it’s Anguish’s wife (Marhaus’s sister) who’s the most upset.  She has the sword-blade removed from Marhaus’s skull and keeps it as a vengeance-token.  Her name: Isoud!  Dun dun dun!  That’s the musical sting you’re hearing now, if you’re at all familiar with the story of Tristram and Isoud (Iseult, Yseult, etc, Malory goes with Isoud in this edition at least so that’s what I’m doing too.)

Actually, she’s the Isoud’s mother, so you have Queen Isoud, and her daughter, the lovely Isoud, who doesn’t get introduced for another chapter or so.