Once they’re at Meligrance’s castle, Guenever’s knights have their wounds bound, which is good, but they’re kept under constant guard, which is bad. No one knows where they went, which is what Meliagrance is counting on! If Arthur and Launcelot don’t know where Guenever is, they can’t rescue her.
Guenever cunningly sends a message to Launcelot via child endangerment. She finds a child of her chamber and gives him one of her special Guenever-courier rings (last mentioned in Book XI) to sneak out and ride away, through the security cordon, across hostile countryside. There’s a tense sequence where the child — again, Malory makes no bones about this kid being underage — heroically steals a horse and rides off. Meliagrance and his guards spot him as he goes, and they give chase, with arrows whizzing by and horses galloping, but this heroic and recklessly endangered kid successfully escapes.
Meliagrance immediately calls all his knights together, and warns them: Launcelot coming is, at this point, inevitable. He outlines some rules of engagement.
1) If you see Launcelot, try shooting him with arrows.
2) If he’s on a horse, shoot the horse with arrows.
3) If he’s on foot and a volley of arrows doesn’t take him down, run away.
4) Do not try to melee with Sir Launcelot under any circumstances, not even if you outnumber him by dozens.
Then he sends out teams of thirty archers to lie in wait along the roads, to guard against Launcelot.
Our heroic child soldier, meanwhile, makes it all the way to Camelot! He finds Launcelot and tells him all about the ambush, Pellas finally justifying his seed, Guenever captured, Meliagrance a traitor, yadda yadda. Launcelot sees the ring and knows the kid isn’t lying, so there’s nothing for it: he tells the kid to let Sir Lavaine know where he went, mounts up, and rides off.
Naturally he comes to the archers’ post. They have a little back-and-forth, Launcelot threatening and the archers threatening and Launcelot calling them campers and so on, and then things get violent. The archers have set up an elaborate earthworks defence for themselves, all ditches and moats and fences, such that Launcelot can’t get up to where they are. Meanwhile they’re laying into him with arrows, killing his horse. So the battle is one-sided, and Launcelot is stymied, which really irritates him.
Seriously, Malory says he’s full sore annoyed as well as full loath to give up. He paces around, all frustrated, just around the corner and out of sight of the archers.
Luckily, just as Launcelot is about to give up, a cart appears!
Launcelot flags the cart down. “Ho there, teamsters! Where are you headed?”
“We’re taking this load of lumber to the castle of Sir Meliagrance,” says the lead teamster. “That was kind of a stupid question. I mean, you can see the cart of lumber right here, and Meliagrance’s castle is the only thing on this road.”
“How about I hop in the back and hide under the lumber, and ride into the castle with you?”
“Yeah, no. No, I don’t think our boss Sir Meliagrance would like that,” replies the lead teamster. “In fact, we should —”
That’s as far as he gets before Launcelot leaps up onto the cart, draws his sword, and slits the guy’s throat. He shoves the corpse out of the driver’s seat and turns to the second teamster.
“I repeat the question.”