There is a feast and songs are sung including "Iron Lances" and "The Queen Took Off Her Sandal, the King Took Off His Crown". The main food is pink lamb.
By using sellswords and knights at the feast disguised as musicians, and getting Robb's men too drunk to fight, Lord Walder Frey is able to coordinate a massacre with little loss to his own men. The two twin castles and the outlying camps are signaled when the band begins playing the "The Rains of Castamere" after the start of the bedding between Edmure and Roslin. Few of the northmen have a chance to react, and most are butchered on the spot.
The Frey and Bolton men turn on the Stark soldiers. Specially-rigged feast tents collapse and are set aflame during the slaughter. In the main hall, many of Robb's personal guard are killed by Freys, including Smalljon Umber, Dacey Mormont, and Ser Wendel Manderly, as well as his mother Catelyn. Roose Bolton personally kills Robb, who was previously shot by arrows, with a thrust to the heart.
Though no definitive count is known, most of the northmen are killed while House Frey loses only approximately fifty men in the camps