Just then! Two riders come up. And they have news: "Your Grace! My lady! The Kingslayer. He escaped in the night!" Robb freaks out: "How? HOW?"
Catelyn's tent! Robb seems unhappy with her. He tells her to tell him "it" isn't true. Ah! It transpires that she set him free to protect her children, because if the word got out that they didn't have Jaime, there'd be nothing to protect Arya and Sansa. And she's also worried about Bran and Rickon, although Jaime doesn't really have anything to do with that. Karstark, who's there with Robb, accuses her of committing treason because her children were prisoners when his children keep dying. He had one die in battle and then Jaime killed the other in his daring escape. And in his view, by freeing Jaime, Catelyn stole his vengeance. She tells him, "Killing Jaime Lannister would not buy life for your children. But returning him to King's Landing may buy life for mine." You can imagine how well that goes over. (The answer is "poorly." It goes over poorly.) Robb says to keep guard on Catelyn and adds another forty men to the forty already looking for Jaime. So she's under arrest and now Robb's splitting his army up to look for Jaime Lannister in addition to fighting the Lannister army and whatever force he sent north to Winterfell. And his war was going so well, too.
Somewhere in a forest, a man falls off a horse. It's Jaime! He's normally a much better rider, but I guess he isn't usually tied up. And he's got Brienne with him! Although since she's not the one who's tied up, I guess really she's got him. He decides that this is the ideal time to make small talk: "What's your name? I'm Jaime Lannister of Casterly Rock." I'm sure she already knows that, Jaime. Brienne admits that she's Brienne of Tarth and he asks if she's the daughter of Lord Selwyn. He's just showing off how well he's memorized the various houses and lords. Then he asks if she's known many men? Women? Horses? She roughs him up a little and lectures him about hurting the innocent. Then she backs off and says, "You will not provoke me to anger!" Jaime laughs at that: "I already have! Look at you! You're ready to chop my head off." He's right, you know. He offers to get into a fair fight with her, but he warns her that only three men in the kingdom could handle him. If I'm following the established pecking order, I think he means Loras, the Hound and someone else. Maybe the Mountain? Anyway, I guess we're supposed to notice that Brienne's already taken down Loras, but that requires a lot of bookkeeping. Brienne makes him get into a canoe. He tries to convince her to be a woman of honor, which presumably involves untying him and giving him a sword. She doesn't bite. She rows him out into a river.