Lord Arnolf Karstark was making his rounds in the castle. He had inspected the blacksmith's newest sword. He had tried the cook's tart and went to speak to the stable master. The stable master was a tall man, he had served House Karstark for 20 years and was proud of that fact, he had bred fine war horses, swift coursers and strong plough horses. Arnolf was talking to the man and as they spoke a rider burst through the gates. He was a guard, the fellow had been part of Karstark's rolling patrols. The fellow reigned his horse. He started to pant and spoke quickly "M'lord. We need help. Me and my men were attacked. It were wildlings. You need to send help. 50 men. They had good steel too. I was the only survivor. We took down 20 men before they over whelmed us. I had to flee."

Arnolf Karstark called for men. He spoke in his battle voice "Collect 50 men. All calvary. We need to be quick." He called for his chain mail and for his axe. With in an hour they were riding off. The party included Arnolf Karstark, his son Harrion and his grandson Benjen Snow.

The party came across the raiders. The raiders had 30 men. They had grabbed some of the Karstark weapons are were attacking a small hamlet. The raiders saw the Karstark men and began to form a basic shield wall. Arnolf called for his men to dismount and they all began to move towards the wildlings.

The battle was long and bloody. Arnolf ended up fighting a tall raider. The two were strong and fierce. But Arnolf had been trained. The raider over swung his great sword and Arnolf used his shoulder to barge the man. The big man fell on his back and Arnolf drove the butt of his axe into the raider's face. Then he felt something pinch his leg. Another raider. It was a woman. She had grabbed a spear and was about to put it through Arnolf's throat. Then he saw it. A giant of a man. Wearing fine ringmail and furs. Carrying a sharp sword in his hand with an axe in his belt. The man brought his sword down on the spear hard. The pointed tip fell to the floor. The woman reached for her daggers but it was too late. The tall man had drove his sword into her belly and ripped upwards. Slicing her into two very distinct pieces.

The tall man helped Arnolf to his feet and fell to his knees. "Lord of the Sun. I am Tormund Shield-Brother. I was one of the men who scaled the Wall. I expected you to be some milk-drinker but you are a brave man. I wish to become one of yours. A sworn sword to guard your back.Will you take me?" Benjen Snow said "Grandsire. I will vouch for this man. I saw him take down two other wildlings before he saved you." Arnolf looked around. All the wildlings were dead. So were 5 of the Karstark men-at-arms. He spoke to Tormund "Very well. I accept you as my sworn-sword. You will be given a place on honour in Karhold"

Arnolf and Tormund headed home.The journey was easy. Tormund had claimed one of the dead men's horses and rode it quite gracefully. The men made stretchers for the 5 dead men carrying them between two horses on pieces of stretched cloth. They died noble deaths and would be buried in the lichyard. Arnolf rode into the castle and called for his steward. "Cregan. Get out here. I want you to find a large room for my friend here Tormund. Give him anything he asks for with in reason. Food, Drink, Arms or Women. I want this man treated well." Cregan hurried off with the wildling in tow. He took Tormund up into the main keep and gave him a large room on the 3rd floor.

TL;DR: Arnolf Karstark welcomes a wilding raider called Tormund Shield-Brother into Karhold as his sworn sword.