Ryman is one of the Frey's sent by Walder Frey to join Robb Stark's cause. When his father dies from a wound received at the battle at Oxcross, Ryman becomes the new heir to the Crossing. After Robb Stark marries Jeyne Westerling and thus breaks the deal he had with the Freys, Ryman leaves Robb's camp withe the Frey men and returns to the Twins. Robb later claims that he might have been able to make amends with the Frey's had Stevron still been alive but that Ryman was far to stubborn to talk to. Ryman participates in the Red Wedding, he kills Dacey Mormont with an axe.
He then leads 2000 Frey men to assist the siege of Riverrun. During the siege he has gallows built right before Riverrun and parades the captive Edmure, claiming that he would hang Edmure should Riverrun not surrender. The Blackfish however doesn't surrender and Ryman has Edmure brought back to camp, only to put up the same facade the next day. When Jaime Lannister arrives to lift the siege, he takes a disliking to Ryman's method as they make him seem weak and sends him back to the Twins. On the way, Ryman's troup is attacked by outlaws, presumably the gang of Lady Stoneheart, and he is killed. When news of it reaches the siege camp, Jaime is bothered by the audacity of the outlaws who kill the heir to the Crossing not far from the Twins. Ryman's son Edwyn suspects that Black Walder is somehow involved in his father's death to become heir of the Twins.