Symond Frey is the seventh son of Walder Frey and the second son of his third wife, Amarei Crakehall. He is married to Betharios of Braavos and has three children, Alesander, Alyx, and Bradamar. Symond is known as a counter of coins and a spymaster.
At the Red Wedding, Symond's oldest son Alesander isn't present, implying he was not happy with the Red Wedding. One of the victims of the Red Wedding is Ser Wendel Manderly, second son of Lord Wyman Manderly of White Harbor, the only city in the North. Symond, a half-brother Jared Frey, and a half-nephew Rhaegar Frey, take Wendel's bones to White Harbor. The Freys wanting to ensure White Harbor supports the Iron Throne, offering the widowed Wyman Manderly a Frey bride, and the marriages of his granddaughters Wynafryd and Wylla Mandery to Rhaegar Frey and another of Walder Frey's grandsons Little Walder Frey.
Davos Seaworth arrives in White Harbor, trying to ensure the Manderlys support Stannis Baratheon. Rhaegar claims that the war is over, Tommen Baratheon is the true King, and they must obey him, saying Robb Stark was a vile dog who died as he deserved, which Manderly agrees with. He then orders his cousin, Ser Marlon Manderly, to execute Davos.
However a common criminal he reassembles Davos is executed instead, and his head and hands, with the fingers shortened, are put on the gate. The head is dipped in tar and an onion stuffed into its mouth (supposedly a mockery of the onion on Davos' sigil) to distort the features further. For this supposed service to the Iron Throne, Wyman's heir is returned. At the feast to celebrate this Lord Manderly tells Davos privately that he was unable to act while his son was a hostage. He tells Davos the Freys are constantly spying on him. He says Symond is always clinking coins, and has bribed several of his servants and two of his knights. One of his wife's handmaids even found their way into the bed of Wyman's fool.
Wyman tells Davos he is planning to restore the Starks, that Bran and Rickon Stark were not killed by Theon Greyjoy, and that he'll support Stannis if Davos recovers Rickon Stark from Skagos. Wyman says he will give the three Freys palfreys as guest gifts, which under the rules of guest right mean they will no longer be under his protection, implying Manderly will have them murdered.
Wyman Manderly and the three Freys apparently leave White Harbor for Barrowton, to attend the wedding of Roose' legitimized bastard Ramsay Bolton, and "Arya Stark" (really Jeyne Poole, who is being forced into the role), to legitimize Bolton rule of the North. However the Freys vanish on the way, Wyman claiming they rode on ahead due to the slowness of his train. Ramsay searches for the Freys but is unable to find them. Roose Bolton has come North with a Frey force and decides to hold the wedding at Winterfell to strengthen Ramsay's claim to Winterfell and force Stannis to battle, Stannis having taken Deepwood Motte and gathered some Northern support. At the wedding Wyman Manderly serves three large pies to the Freys and Boltons, which include Rhaegars' father Aenys Frey, eating some himself. Wyman asks for a song of the Rat Cook, who served to a King who had wronged him a pie containing his son. He was punished by being turned into a rat that could only eat its children for murdering a guest. These imply that the missing Freys were present at the wedding after all. Big Walder Frey thinks that Wyman had the Freys travelling with him murdered, and later Hosteen Frey accuses Wyman of their murders, which Wyman laughs at.