Primary Sources: Le Morte D’Arthur, Book X, Chapters 7 and 8
So Mark as you hopefully recall is the king of Cornwall. He’s not Arthur’s vassal but neither is he Arthur’s enemy. Mark’s nephew Tristram loves the lovely Isoud, and been exiled from Cornwall; as of last chapter he resides at Camelot. The lovely Isoud is Mark’s wife, Tristram’s mistress, queen of Cornwall and princess of Ireland. The whole Isoud/Tristram thing is what prompted Tristram to leave Cornwall, ultimately. Also Mark kicked him out, which was not a popular move among the Cornish knights.
Mark learns Tristram has joined the Round Table and he doesn’t like this one bit. This whole neither Arthur’s enemy nor his vassal thing is a very fine line to walk, and Mark figures it’s just a matter of time before Arthur gets tired of Cornwall not being part of his empire. He sends spies to Camelot, to check up on Tristram. The lovely Isoud sends more spies, to bear Tristram love letters. It’s a whole Cornwall crisis!
Finally Mark can’t take it any more. He sets out for Camelot. He takes along two henchmen, Bersules and Amant, and their squires, and disguises himself as a random guy who isn’t the king of Cornwall.
“Here’s the plan,” Mark tells Bersules and Amant. “We’re going to defeat Tristram, somehow. Maybe kill him, maybe just ruin him, I dunno.”
“Wait, murder?” asks Bersules.
“Yeah murder,” snaps Mark. “I’m the villain!”
“I didn’t realize I was signing up for murder,” says Bersules. “I’m just going to back out now, if you don’t mind…”
But Mark does mind! You can tell, because Mark cuts Bersules’s head off.
“Whoa,” says Amant.
“Whoa,” says Amant’s squire.
“Whoa,” says Bersules’s squire.
“Ha,” says Mark. “I’m in charge, you hear me?” He brandishes his sword at the other three.
Amant and the squires exchange glances, and then all three draw their own swords. “We respectfully resign from your service,” they chorus.
Mark almost tries to kill all three of them at once, but he’s not an idiot. They’re on guard and they’ve got him outnumbered. So he lets them go, but demands that they not warn Camelot and especially not mention that he’s the king of Cornwall.
Amant and the others agree to this, probably more out of concern for Cornwall than for Mark. They watch Mark run off, and then give Bersules’s body a decent burial.
Later Mark stumbles across a knight crying in the woods.
“Unh, so unfair,” Mark mutters. “I’ve fallen into a strange adventure.”
“Ooooh,” sobs the knight. “Oooooh, sweet Queen Margawse of Orkney. Ooooh, Lot’s wife. Oooooh, mother of Gawaine and Gaheris and grandmother of Sir Gingalin, a full-grown knight last seen in Book IX Chapter 18! Oooh how I wished you loved me the way you love your grandson who is roughly my age!”
Malory does not point out the massive age disparity, I admit.
It’s Sir Lamorak! King Pellinore’s son and regular visitor to Mark’s court at Tintagil. Adventured with Tristram several times in Book VIII and Book IX. His love of Margawse is well-established, as of Book IX Chapter 13.
However Lamorak doesn’t recognize Mark, when Mark sidles up at offers a sympathetic ear. Lamorak can tell he’s Cornish from his accent, though, and launches into a wholly unrelated spiel about what a terrible country Cornwall is.
“You know they kicked out Sir Tristram? Really I shouldn’t bag on the whole nation, it’s that idiot King Mark who’s to blame, you know.”
“Oh ah.”
“That Mark, he is the shamefullest king that is now living… a great enemy to all good knights… it is a pity that ever any such false knight-coward as King Mark is, should be matched with such a fair lady and as good as the lovely Isoud is.”
“Listen,” Mark says. “I haven’t been back to Cornwall in years. I know I have the accent but really all this has nothing to do with me.”
“Well, that’s good,” says Lamorak. “If I thought you were some kind of filthy pro-Mark partisan, I don’t know what I’d do.”
I give the whole story points because of the whole moral ambiguity involved. On one hand, going off to murder Tristam is bad, on the other I’m leery of an argument which has at its root “Why can’t you be nice to your wife’s boyfriend?”