Book III is the tale, apparently, of Arthur’s wedding to Guenever. Malory starts off by reminding us of a few salient points:
1) Arthur is a young and unmarried king.
2) When he became king, a bunch of folks — Team Lot & Mister 100, for instance — refused to accept his authority because they didn’t know he was Uther’s son.
3) Merlin (and Igraine, Arthur’s mother, who doesn’t show up again I don’t think) eventually got around to telling everyone about how Arthur was Uther’s son.
4) Arthur is under the impression that Merlin is a wise dude whose advice should be followed. In fact one might assert that Arthur doesn’t go to the bathroom without Merlin’s go-ahead.
So one day Arthur comes to Merlin. “I’ve got a new project I want to get started,” he says. “Tell me what you think of this.”
“It’ll all end in tears,” says Merlin. “But go ahead.”
“Okay, so, really it’s the guys putting me up to this, they’re all the time ragging on me about how I only have illegitimate children and mistresses, and not a wife and legitimate kids like a king oughta,” says Arthur. “I’ve been toying with the idea of just keeping a stable of mistresses, though.”
“No, you should marry,” says Merlin. “Guy like you, king of England, magic swords, madcap killing machine, you would be a great husband.”
“Yeah, well, I like mistresses,” says Arthur. “But okay. I need to marry a lady, let’s see, I’ll need to get a hall, a new suit, a priest…”
“And a wife,” says Merlin. “You have to marry a particular woman. Do you have one in mind?”
“Oh, yeah, right,” says Arthur. “I do have a lady in mind, actually. By my reckoning she’s the best lady: Guenever the valiant. You remember her? King Leodegrande’s daughter? Apparently Uther gave Leodegrande a table, years back, I’m hoping I can get him to throw it in alongside the daughter.”
“Really? Her?” asks Merlin.
“Yes!” says Arthur. “She’s valiant and it’ll tighten up ties with Cameliard and North Wales, which is important if I ever want to not being at war.”
Merlin sighs, heavily. “I can see your mind is made up. I’ve been putting together this report, the Top Fifty Reasons Arthur Should Marry Someone, Anyone, Who Isn’t Guenever, complete with plenty of photos of other fair and valiant ladies, but I’m too late.”
“You bet my mind is made up!” says Arthur. “Famously valiant, peace in the west, my father’s old table, and when we met that one time she seemed nice enough.”
“So now you’re going to marry her, and she’ll cheat on you with Launcelot…”
“La la la I’m not listening!” cries Arthur, and plugs his ears up. “Besides half your predictions are crazy nonsense anyhow, I don’t feel obliged to pay attention them.”
“Fine, fine,” says Merlin. “All right, we’ll do it your way. Here’s what we do. I take some of your knights with me to Cameliard, where King Leodegrande is, and I’ll set it all up.”
So Merlin goes to Cameliard and meets with Leodegrande, and tells him about Arthur’s interest in his daughter.
Leodegrande couldn’t be happier. “Arthur the king of all England wants to marry my daughter? Sign me up! He’s the Most Eligible Bachelor in Britain! I can’t wait to welcome that MEBIB into the family! Should I sign my kingdom over to him?”
“Okay, okay, calm down, hold onto your horses,” says Merlin.
“I know, I know, he’s already king of all England, what would he want with the throne of Cameliard…”
“You can keep the throne,” says Merlin. “But there is one piece of furniture Arthur’s interested in.”
“Merle, I know it’s medieval times, but my daughter is not literally a piece of furniture. No,” says Leodegrande. “I’ll send him the Round Table.”
“Great,” says Merlin. “That’s what I came here for.”
“I’m not using it myself,” says Leodegrande. “It seats one hundred and fifty, and I’ve only got a hundred knights left since the whole Rience affair.”
“Enh, we’ll take them too,” says Merlin. “Can’t have too many knights.”
So Merlin loads up the Round Table and Guenever (who pretty clearly gets zero say in this whole affair, most valiant lady in England or no) and the hundred knights and hauls the whole kit and caboodle back to London, because Malory can’t keep straight whether Arthur lives in London, Caerlaeon, or Camelot.