Catelyn and Brienne see Ser Edmure off as he leads his men out of Riverrun to do battle with Lord Tywin. He has left only a small garrison of the young, old, and wounded led by Ser Desmond to defend the castle. Brienne asks what they must do now, and Catelyn responds they will do their duty. Catelyn has always done duty, making her Lord Hoster's favorite child. Since her two older brothers died in infancy, Catelyn was a son and a daughter to him until Edmure was born. She was forced into being lady of Riverrun at an early age when her mother died, snubbed Petyr when she had to marry Brandon Stark, and married Eddard without complaint when Brandon died. Catelyn ends up praying in the sept for hours. She thinks of some of her mentors like Lord Hoster, Ser Brynden, Septon Osmynd, and Maester Kym and laments that they always seemed to know everything, while for the first time in her life she is unsure of her duty. When she emerges, she sees Rymund singing a song about war. Brienne stops to listen and wishes she were fighting in the battle. Later that day, Maester Vyman receives a raven from Lord Elwood stating that Ser Cortnay is dead and that Storm's End has declared for Stannis. Catelyn asks where Robb is so he can be told, and Vyman responds that he was marching for the Crag, the seat of House Westerling, at last report. Ser Desmond's squire comes to report that Lannisters have reached the river. Catelyn goes to the battlements to join Ser Desmond. About fifty Lannister scouts flying the purple unicorn of House Brax are on the far side. The ford, as well as three others, are held by Mallister men. After a brief skirmish, the Lannisters withdraw. There is another attempt at the ford late that night, but it holds again. Brienne says that Tywin is probably probing for a weakness and will try to force a crossing if he cannot find one open.

The next morning, Catelyn tells Utherydes to send wine to Ser Cleos to soften him up for questioning later. Soon after, a rider comes with a message from Lord Jason. Ser Flement tried to force a crossing at another ford but was turned aside with heavy losses. Lord Karyl also repulsed another attack even further upstream. That evening she visits Ser Cleos and asks him about the peace terms he brought, which he divulges. Catelyn is particularly interested in Tyrion's promise to exchange Arya and Sansa for Jaime. She asks after her daughters and discovers that Cleos never saw Arya. Five days later, Catelyn learns that Tywin launched his major assault two days before. He tried to force a crossing at a dozen different fords. Lord Leo Lefford drowned and Ser Lyle Crakehall, known as Strongboar, was captured. Ser Addam made three attempts at one ford, but was finally forced to retreat. At Stone Mill, Ser Gregor led the fiercest assault, and a few of his men briefly gained the other side, but the reserves were committed, and he was forced to withdraw. Lord Tywin is now moving southeast and appears to be in retreat. A great celebration is held that night, but Catelyn is worried. She goes and pulls out some maps and sees that if Tywin is heading southeast, he has probably already reached the headwaters of the Blackwater.