Primary Sources: Le Morte D’Arthur, Book X, Chapter 12
Dinadan and the other knights from Camelot stay up late, drinking and swapping Launcelot stories, and eventually Dinadan notices that Mark never came down to the party. He pokes around, and finds him hiding in a closet.
“What are you doing?!” Dinadan demands.
“I’m hiding from all the knights! How did you escape?”
“…They’re friends of mine.”
“We were drinking, talking…”
“Who’s out there?”
“Launcelot,” lies Dinadan.
“Launcelot! Ooooh nooo!” Mark quakes in his boots. Malory wants us to understand, in case he’s been too subtle to this point: Mark is a coward and a murderer and a coward. “Are you sure it’s him?”
“Yeah. He’s wearing his shield that says PROPERTY OF MORDRED on it, that’s how you know it’s him. Now are you going to come out and join the party?”
“Let’s ride away from here,” says Mark. “Right now.”
“What? You promised! You promised that you’d escort me!”
“That was before you ran away and hid from me. That discharges all obligations. No more escorting.”
So when the knights from Camelot ride off in the morning, Dinadan rides with them, leaving Mark behind.
“What was up with that Cornish coward?” someone asks Dinadan.
“Don’t waste time thinking about him. I told him Mordred was Sir Launcelot and he was all ooooh nooo!” Dinadan does a passable imitation of Mark’s quaking.
“You told him I was Launcelot?” asks Mordred.
“Well, I told him your shield was his.”
“Ah. Pity I’ve got this broken arm, which Malory didn’t mention before and won’t mention again. Otherwise I could give him a good scare.”
“I’ve got an idea,” says Sir Griftlet. “Let’s get Sir Dagonet to wear it!”
Sir Dagonet, as you have probably forgotten, is Arthur’s jester. He may or may not be a good knight, because all he’s ever called upon to do is pratfalls. He’s extremely skilled at pratfalls.
“Sounds good,” says Dagonet, who was also there, Malory hastens to tell us.
So Dagonet takes Mordred’s gear and waits by the road while the other knights hide behind trees. After a little while, Mark ambles up the path.
“Stop, you Cornish knight, you!” cries Dagonet in his spookiest voice. “I, Sir Launcelot, shall joust you!”
Mark squeals, flees, and everyone who isn’t Mark has a good laugh. They chase him around for a while, banging on their shields, and laughing, until all the forest rang of the noise. Mark has no idea what’s up, he’s getting chased by Launcelot, he just keeps zooming off.
Dagonet chases Mark, because he’s not one to let a joke just drop before it’s been hammered all the way into the ground, and eventually Dinadan and his friends have to chase after Dagonet who’s chasing Mark. They don’t want Dagonet to actually catch Mark and joust him, because there’s an outside chance Dagonet would get hurt.
And then Arthur would be pissed! Dagonet is Arthur’s favorite comedian. According to Malory he does a routine at the start of every tournament Arthur attends, which never fails to make Arthur laugh.
Man, you think they’d learn from Patroclus. Trying to pass as someone more badass than you are? Never works out.