Having received word of Bran and Rickon's deaths, Catelyn is depressed in Riverrun.
She tells Brienne, sadness becoming icy hatred as she swears Robb will avenge all her family's wrongful deaths.
At midnight, Catelyn and Brienne visit Jaime Lannister in his cell. Jaime welcomes them to his abode—although after about a year of imprisonment, he's not looking so hot.
He agrees to answer her questions if she will answer his. Jaime admits to being the one to push Bran off the tower, but he swears he did not send the assassin to kill the boy—he may have attempted child murder, but that's just not his style.
During their conversation, Catelyn realizes Littlefinger lied about Tyrion's dagger, too. Frankly, we're surprised she's surprised that Littlefinger's a gamer and a schemer. But anyway.
Catelyn wonders how Jaime could consider himself a knight after all the vows he's forsaken, but Jaime contends that it is impossible to maintain all those vows when they come into conflict with each other.
Drunk on wine and getting talkative, Jaime tells Catelyn the story of how Rickard and Brandon Stark, Eddard's father and elder brother respectively, were executed by King Aerys.
The tale shows that Aerys was aptly named the Mad King. Jaime may be named Kingslayer, but he'd argue the king might have needed some slaying.
When Jaime brings up the topic of Eddard's illegitimate son, Catelyn asks Brienne for her sword.