Arn Kalapunki undertakes the oath to defeat Thaugolos, the Scourge of the Mountains, to avenge and free his people from the village of Wolfstone.
After proving his bond to Jorunn by dealing with Oddgeir, she gave Arn vital information about an ancient magical spear that their grandfather Vestlidi once wielded against Thaugolos, wounding it. This is the reason the dragon returned and visited destruction upon Wolfstone. Ulvetann was stolen by the forester Irsia as she believed it could cure a great evil.
He traveled to Highmark to gain passage to the Barrier Islands where he believed the spear to be, only to find Highmark destroyed. This sent him on his way to rescue the people of Highmark with the hopes of finding Ulvetann along the way. Arn accomplished both, fulfilling a vow and taking possession of the broken spear.
He set out in search of a blacksmith to repaur Ulvetann, traveling into the Deep Wilds where he met Balathu who took him to the Elvish settlement of to repair the weapon, as they too had been harried by Thaugolos and wished the beast dealt with once and for all.