In the saga, Halfdan flees his father's kingdom after an attack by the Viking berserker Soti, and goes to live in exile in Bjarmaland.
During a sea-voyage he is dragged off course by the witchcraft of a troll named Járnnefr (Iron-Nose) and shipwrecked on the shore of Helluland.
Halfdan encounters a troll-woman named Brana who is really the daughter of the king of Valland, who was abducted by the troll Jarnhauss (Iron-Skull) and transformed into her current shape.
She asks Halfdan and his friends to avenge her by killing Jarnhauss and his fellow trolls.
In return, she provides them with shelter, and gives Halfdan a magic ring, a coat that makes him invulnerable to edged weapons, and a dragon-ship.