Arno was the brother of Deerkin who was also joined the Piebalds, even though he did not possess the Wit.
After the Piebalds fled Galekeep with Prince Dutiful, they end up getting in a fight with some townspeople. Arno sacrifices himself so that the others can escape. Even though he is not witted the townspeople kill him using the traditional method for witted people: Hanging him, chopping him to pieces, and burning the pieces over water.
After Deerkin realizes the errors of his ways he spies on the Piebalds for the Old Bloods in memory of his dead brother.