 The Stark army arrives at the Twins , a fortified bridge stronghold controlled by the cranky Lord Walder Frey ( David Bradley ) , who is nominally sworn to Catelyn 's ( Michelle Fairley ) father Hoster Tully . However , Lord Frey has sealed off the bridge and refuses to let the army cross , so Catelyn negotiates on her son Robb 's behalf . After some hard bargaining , Frey agrees to allow the Stark army to cross through The Twins and to commit some of his troops to the conflict with the Lannisters , but , in return , he wants Robb ( Richard Madden ) and his sister Arya ( Maisie Williams ) to marry two of his children , to which Robb reluctantly agrees . 
