Quick recap: Arthur and his court are up by the Humber, and the five kings he’s at war with have been told where he is. They take the one king’s brother’s advice, and ride out to sneak-attack Arthur before he gets all his reinforcements together.
Meanwhile, Arthur’s setting up his camp, and he’s lounging, all relaxed with Guenever, and Sir Kay gets worried. “I dunno, bro,” he says. “We could get sneak-attacked at any point, maybe we ought to be sleeping in armor and stuff.”
“You worry too much,” says Sir Gawaine.
“We’ll all be fine,” says Sir Griftlet. Gawaine and Griftlet and Kay are all the named-character knights Arthur has with him right now, and they’re drinking and playing cards.
And, you know, it’s not like Malory hasn’t pulled this stunt before, but as soon as Kay expresses concern, sure enough, sneak attack by the enemy. This is the one dramatic-irony trick Malory knows, and he plays it over and over again. Arthur’s camp is thrown into disarray, folks start blaming one another for giving away their location, it’s a bad scene. Arthur and Kay and Gawaine and Griftlet all armor up as quick as they can, but still, before they’re ready to join battle it’s pretty much over. One of Arthur’s men rides up, all bloody, and says “Sire! Sire! All is lost! Save yourself!”
So Arthur, Kay, Gawaine, Griftlet, Gawaine’s perpetual guard of scolding ladies-in-waiting (I assume), and Guenever mount up and ride away, hoping to avoid capture by the enemy. They ride out in the wrong direction and hit the Humber, and the tide is in I guess because it’s way too deep for their horses to ford, so, no luck.
“Well, shoot,” says Arthur. “We’re out of luck here. Guenever, do you think we should stand here and fight, or try to swim across?”
“On balance I’d rather drown than have all the terrible things that would happen to me if I were captured happen to me,” says Guenever. “So let’s go for the water.”
Meanwhile, though, Kay has been keeping his eyes open, and he sees five knights riding up. He squints, he looks, are they friends or foes? Foes, it turns out, and not just any foes! It’s the five kings themselves, who got separated from their main force somehow and decided to track down Arthur instead of rejoining their armies.
“We’re in luck, guys!” Kay exclaims. “There’s five of them and three of us. Four of us, counting Gawaine.”
“I don’t like those odds, five on three,” says Gawaine.
“Tell you what,” says Kay. “I’ll kill the two in front, and then the rest of you can handle the survivors in an even matchup.”
Long story short, they actually pull this off: Arthur, Gawaine, and Griflet each kill one king, and Kay kills two. (Also, I am not making up the bit about Gawaine. Let me quote Malory: “That were folly, said Sir Gawaine, for we are but three and they be five.”)
“Good job!” says Guenever. “Good job Arthur, good job Griftlet, acceptable job Gawaine. Extra-good job, Kay! I’m not just saying that because you’re my brother-in-law. You get MVP for this battle. I’ll have to find you a wife.” At this point the group splits up: Guenever and the ladies-in-waiting take a barge across the Humber, while Arthur and the knights go looking for the remnants of Arthur’s army.
It turns out Arthur’s army is just over the next hill, in the woods, all licking their wounds and wailing about how badly they got beat. Arthur cheers them right up, though, by telling them about he and Kay and Griftlet and Gawaine defeated the opposition in a single surgical strike, thanks not so much to tactical skill as dumb luck. So Arthur rallies his troops, and meanwhile the other side’s troops find their generals’ bodies, and they wail and weep and are wholly demoralized, and boom, in comes Arthur with a small death squad and they kill a few thousand guys and disperse the rest. Arthur takes a knee and thanks God. Guenever and her ladies come back, and Guenever congratulates all the knights on a job well done.