Long story short, Gareth wins, although he’s injured in the process. The Black Knight is slain, and Gareth claims his horse and changes into his armor (which is, apparently, nicer than the armor that Peter supplied Gareth with back in chapter III) and catches up with Linet, who tried to ditch him again.
“Go away, Prettyboy, you stink of jousting and bloodshed. Alas! That such a knight as the Black Knight should die of a sudden brain aneurysm in the middle of jousting a churl such as yourself. Or maybe he had a stroke. In any case, you’re a jinx. For your own good, I beg you Prettyboy, go home before you’re killed.”
Gareth sighs. “I may be slain, but unless that happens, I’m sticking with you on this strange adventure, Linet. You keep saying I’ll get myself killed, and it’s my foes who keep ending up on the ground. Not that it keeps you from chastising me.”
And okay, this is getting repetitive, so I’m going to sum up. Basically Gareth and Linet move on through the Black Lands and arrive in the Green Lands, where they meet the Green Knight, who wants to avenge the death of his brother the Black Knight, and there’s a green horn and a green shield and a green spear and green banners and so on. And it basically goes just like the last encounter, except that at the end, this time, Gareth has the Green Knight on the rocks, and the Green Knight surrenders.
“I’ll accept your surrender and grant you your life only if milady chooses to accept it,” says Gareth. “Linet, do you wish I should spare this knight his life?”
And Linet refuses, on the grounds that the Green Knight is not actually in danger, because although Gareth has him on his knees with his helmet off, surely the Green Knight is actually winning, Because he’s a knight, and Gareth is a kitchen boy. There’s a bit of tension here: will Gareth just kill the dude, then?
But no. It all works out. The Green Knight surrenders and he treats Gareth and Linet to a huge dinner. He tells Gareth that he and his vassals will be at Gareth’s service, and you might think this would impress Linet, but only if you haven’t been paying attention up to this point. She goes off on this whole spiel about knights who are better than Gareth — some we’ve heard of, like Launcelot and Tristram, and some we haven’t, like Wade and Lamorak. One last time she tries to talk Gareth into going home, and one last time he refuses. And so they come, at last, to the Red Lands, and the Pass Perilous.