Appearance and Character
A Storm of Swords
Harwyn and his brothers, Ser Dennis and Ser Peter, are among the men sent by Lord Tywin Lannister to the riverlands in search of his son, after Ser Jaime Lannister has been released from Riverrun by Lady Catelyn Stark.
A Feast for Crows
Harwyn considers the tales that Lord Beric Dondarrion cannot be killed to be lies. He promises Lancel's wife, Lady Amerei, whose father Merrett Frey was hanged by the brotherhood without banners, that he is going to bring her Beric's head. He believes the smallfolk in the riverlands secretly hide and support the brotherhood, lying about this to their lords.
Upon hearing reports that there are outlaws on the other side of the Trident, Harwyn takes five knights and twenty archers and goes searching for them, making him miss Ser Jaime Lannister's visit to Darry when Jaime is on his way to ending the siege of Riverrun. Jaime suspects that "Gatehouse Ami" has an amorous interest in Harwyn. When Jaime warns Lancel, his cousin expresses his indifference, announcing that he is going to renounce lordship and marriage in favor of joining the Warrior's Sons and that Harwyn can have both, if he wants to.
—thoughts of Jaime Lannister
Jaime: Darry needs a lion, coz. So does your little Frey. She gets moist between the legs every time someone mentions Hardstone. If she hasn't bedded him yet, she will soon.
Lancel: If she loves him, I wish them joy of one another.