What's the deal with Cat's resurrection
at the end of Storm of Swords?

The epilogue of A Storm of Swords provides a shocking twist of events for the reader--Catelyn Tully Stark, believed to have been killed at the Red Wedding, appears with three members of the Brotherhood Without Banners, alive if not necessarily in the healthiest condition. But what really happened? How did she get there from her death hundreds of pages earlier? For the astute reader, some facts can be ascertained.

First, let’s clear up some misconceptions that get tossed around every once in while. Yes, Catelyn was killed in the Red Wedding. And yes, she was alive at the end of the book, as opposed to having her dead corpse being used as some puppet to freak Merrett out. Both these facts can be confirmed by one of the prophecies of the Ghost of High Heart, on SoS, pg. 249:

“I dreamt of a roaring river, and a woman who was a fish. Dead she drifted, with red tears on her cheeks, but when her eyes did open, oh, I woke from terror.”

Catelyn is clearly the fish (the trout is the sigil of House Tully). So it seems she was definitely dead, and resurrected somehow. So what happened between the Red Wedding and the end of the book that caused this strange twist of events?

After Cat was killed (SoS, pg. 583), the first notion of what happened to her comes from something Tyrion thinks on SoS, pg. 654

Sansa did not need to know how her brother’s body had been hacked and mutilated, he decided; nor hwo her mother’s corpse had been dumped naked into the Green Fork in a savage mockery of House Tully’s funeral customs.

So it appears that Catelyn’s body was dumped into the river. What happened to her then?

The next piece of the puzzle comes from Arya. On SoS, pg. 730, Arya is having a wolf-dream through Nymeria’s point of view. She trots down to a river full of rotting corpses. Smelling her mother, the wolf races into the water and drags out the naked corpse of a woman. A woman with “cold blood trickling from her throat,” a wound which sounds surprisingly similar to the one that killed Catelyn. However, after the corpse is laid down on the bank, Nymeria sees men with swords coming toward the river, and runs off, leaving the corpse behind.

There can be little doubt that this corpse was Catelyn. When Arya wakes up, she tells Sandor that she dreamt of her mother.

So now we have Cat’s corpse on the riverbank, and men riding toward it. These men are almost certainly some outlaws of the Brotherhood Without Banners, as Cat is with three of them (Lem Lemoncloak, Tom o’Sevens and Jack-be-Lucky) at the end of the book. The one key member of the outlaw band, however, is Thoros of Myr. Thoros has already been known to raise Beric from the dead several times. Could he have done the same to Cat? Most likely. He probably was one of the men who found the corpse, prepared to give the rite of the Last Kiss, and found Cat coming back to life as Beric has done. There is no other even remotely plausible option.

Most people are usually not brought back to life by the Last Kiss. Thoros tells Arya on SoS, pg. 444, that Beric was resurrected because “R’hllor is not done with him yet.” Evidently, R’hllor is not done with Catelyn Stark either. Only time will tell what crucial part she has to play in upcoming events.