The Brotherhood Without Banners (in Riverrun)

Catelyn whispered into the boys ear and he relayed the information once more. “No one can be safe until the Twins burn.” He said, finally. “The Freys are vile they will keep coming.. and coming.. until there’s nothing left. But, your plan is not a terrible one. Do you think you could get us inside like this? You yourself said Walder is a suspicious old monster.”

After a long moment the silence was broken. “Life..” Catelyn croaked, in her uneven and foul voice. Some of the brotherhood begin talking to one another, in hushed tones. The Northman boy looks to Jaime. “You’re a lucky one, Lady Stoneheart never spares a target.” He crosses his arms. “How much livery can you get your hands on? Do you think we could enter as a troop, assuming you could get enough of it? Perhaps the women might disguise themselves as silent sisters?” He paused adding. “We’ll need your oath to, whatever that may be worth.”

Lady Catelyn looked to Brynden to hear his piece. “And how will our forces know to head for the Twins? We aren’t exactly friends in that land.” The Northmen said to Jaime.

"The twins stand as one of the best defended castles in all of Westeros, but most of those defenses will be for naught against men from the inside. I suggest we move on the Twins first, as they are the harder prize as well as the seat of the chief brain behind all Frey activity. If we take Riverrun first, it leaves Old Walder both alive and with time to prepare once word reaches him. If we can
clear out the Twins, the head is cut from the snake," he mimed a slashing motion with his hand as he spoke, "And then Riverrun will be left more vulnerable - not for lack of defenses, it is at least as well fortified as the Twins, but rather for lack of direction. Any of the lesser Freys will be easier to intimidate and manipulate into turning the castle back over." He seemed to be drawing out a map in his head as he spoke, connecting the lines of this plan that was formulating.

"I imagine this particular serpent is more likely to retreat into his hole and never emerge again, but I suppose he can't take the Riverlands if he hides away in the Twins forever, and once we have the rest of the Riverlands on our side we can deal with him." He narrowed his eyes and peered at Jaime, "You've worked with him, you know this particular serpent. I will yield to your judgement on this, Lannister, but if you're wrong and we still live, I'll make sure you don't make it out of the Riverlands alive. We'll take Riverrun first, so long as no one else disputes that course of action."

A maester, who was captured from Riverrun, reveals all that he knew of what has transpired to Mother Merciless. She and her confederates learn of Lord Baelish being named Lord Paramount by King Tommen. Furthermore, of how Sansa Stark requested the levies be raised, in the name of her warden, Lord Baelish, in order to fight the pretender Stannis Baratheon. A parchment was shown revealing the raven's note involving the former as well another bearing a rally from Edmure Tully, which had been disregarded by the Freys. There were more messages after that. The maester informed them of a battle between two camps of the Riverlords that had happened upon the Trident. He did not know where they were, but one side was for Edmure, led by Harlton and Shawney, and the other for Baelish, led by Lord Blackwood. It seemed that the Riverlands were in quite a disarray.

A more recent raven revealed a new piece of information: Lord Baelish had given up the Lord Paramountcy to the returned Edmure Tully after bending the knee to Stannis Baratheon in the Vale.

Given this information, Catelyn Tully had some options to play with, especially given the still ongoing battle somewhere around the Trident.