Game Of Thrones: 10 Storylines From The Books The Show Ignored
9. Lady Stoneheart Takes Revenge
For the most part, the Red Wedding of the show follows the source material relatively closely. There are some minor differences, Robb's wife (named Jeyne in the books) is neither pregnant nor present for the wedding, but the key points remain. Robb, his mother, and his northmen are slaughtered while attending the wedding at the Twins.
It is after the wedding that things take a different turn in the books. The Brotherhood Without Banners soon after take on a mysterious new leader by the name of Lady Stoneheart, with whom they hunt down and hang anyone connected with the Red wedding.
It turns out that Lady Stoneheart is the re-animated and decaying corpse of Lady Catelyn Stark, brought back to life by Beric Dondarrion and Thoros of Myr when they found her three days after the wedding. Hellbent on revenge with no regard for the consequences, Lady Stoneheart roams the Riverlands killing any Frey, Bolton, or Lannister she can find.
The last we see of her in the books, she and the Brotherhood have captured Brienne, and have sent her to set a trap to catch Jaime Lannister. Against her better judgement Brienne obliges, but only because she and her companions, Podrick Payne and Ser Hyle Hunt, will be killed if she doesn't.