When Tristram gets to Arthur’s pavilion, Arthur has already heard about him. We flash back a couple of seconds!
“Uncle Sire!” cries Gawaine, just before Tristram arrives. “This knight came and beat up me and a bunch of my associates!”
“Oh?” Arthur perks up. He’s always happy to hear about someone hitting Gawaine. “Who?”
“That guy, Uncle Sire!” And Gawaine points to Tristram, who’s just come in. Flashback over!
“Okay. Great. Guy in a distinctive face-concealing helmet, you there! What’s your name? Are you someone I know?” asks Arthur.
“Not telling,” says Tristram, and leaves. What a jerk!
“Go bring him back,” Arthur tells the closest knight who isn’t Sir Gawaine. This turns out to be Sir Griftlet.
Griftlet runs after Tristram and fetches him back.
“I’m only back on the condition that you not ask my name,” says Tristram.
“Okay. Whatever. Is there a reason you won’t tell me your name? Or is it cheating to ask that?”
“Sir, without a cause I would not hide my name,” says Tristram.
“So you have a reason, okay. And that reason is….?” Arthur gestures for Tristram to complete the sentence.
Tristram remains obstinately silent, however.
“Okay, whatever, I don’t really care about this. Have you picked a side in the big me versus all the other kings thing that’s happening this tournament?”
“Mmmmaybe,” says Tristram.
“You’re just being a jerk for no reason,” grumbles Arthur. “I’d think you were Tristram or something.” (He does not actually say that bit.)
And then a lot of jousting happens. Sir Gareth jousts Mister 100’s nephew Sir Selises. Knights who aren’t Scottish joust knights who are. It’s a big chaotic mess.
“Who are all these knights?” asks Arthur, watching. “Are some of them my knights? I can’t even keep track. Launcelot, do you have any idea?”
Launcelot shrugs helplessly. Arthur scowls and turns to Kay.
“Kay, run out and do a head count. Are we missing any knights of the Round Table?”
Kay does a quick count, and confirms that Arthur’s company is short ten knights. Tristram, Palomides, Percivale, Gaheris, Epinogris, Mordred, Dinadan, Breunor (aka Sir Ill-Fitting Suit), and Nimue’s husband, Sir Pellas. Which is nine knights. Because Malory can’t count. He does this all the time.
Some of Gawaine’s lesser cousins, Edward and Sadok, joust on Arthur’s behalf against the kings of Scotland and North Wales, respectively, and win, which vexes Sir Palomides. Palomides is on the side of the Scottish king, along with Tristram (who changed his mind about the whole working for Arthur thing). The two of them engage various of Gawaine’s relatives, including but not limited to Edward and Sadok.
“Who are those guys?” asks Arthur, but no one can tell him. He watches as Tristram and Palomides just lay waste, in their fight against the Orkney faction. “Man that is some quality jousting!”
Arthur points at Tristram. “Whoever that guy is, he’s like to a wood lion.” He points at Palomides. “And him? He’s like to a wood leopard. But Gawaine and his cousins, they’re all things that get badly defeated by wooden animals. That was an analogy that kind of got away from me. Good thing I’m basically just talking to myself…”
While Arthur talks to himself, Gawaine and the rest of the Orkney knights decide that getting walloped by anonymous Scots knights (secretly Tristram and Palomides) isn’t any fun at all, and go off to sulk.
Then Arthur talks Launcelot into taking on Tristram, putting together a scheme wherein Launcelot fights the one knight (Tristram in disguise), Bleoberis fights the other knight (Palomides in disguise), Ector the Lesser fights the other other knight (Gareth in disguise) and finally Arthur himself fights the last knight of the mysterious foursome (Sir Dinadan, also in disguise).
Long story short, Arthur’s team is winning, and then the King of Northgalis decides to rescue Tristram, which he does, and then Tristram dehorses King Arthur. Then Tristram runs away and changes clothes. Instead of a Green Knight disguise, he dons a Red Knight disguise.