Inside Winterfell, the obnoxious Ramsay Bolton has already figured out Sansa and Brienne's plan, and tells his father Roose that he's going to storm Castle Black, kill Jon Snow, and take Sansa back. Roose thinks this is an awful idea because it will turn the North against the Boltons. Ramsay rebuts that they don't need everyone, just the Umbers, the Karstarks, and the Manderlys. Thanks to the handy reminder in the "previously on," we know the Karstarks hate the Starks because Robb murdered their lord. Thanks, "previously on." It seems like his plan should work.
Roose tells Ramsay, "If you acquire the reputation of a mad dog, you will be treated like a mad dog, taken out back, and slaughtered for pig feed." This, and the news of the birth of his new baby brother, pisses Ramsay off so much that he slays his father and then feeds his stepmother and half-brother to his dogs. What is up with Ramsay Bolton and dogs? I've heard of Crazy Cat Ladies before, but a Psychopathic Dog Man is a new one.