Avella's father owed a debt to The Dark One. In exchange for his absolution, her father offered The Dark One his firstborn, which turned out to be Avella. Avella's skin was marked by mystical runes, enabling The Dark One to call upon Avella for whatever and whenever he wishes. Wanting the runes removes from her body, she sided with Gisbourne. He promised that if she did a task for him, he would remove the runes.
Major Story Arcs
After the Realm War, the Dark One helped the Cabal do a spell that made everyone forget about the Realm War. For one not bound to linear time, the spell drove Avella crazy. Avella was used by the Cabal to attack Marian Quin. Due to the spells of Sam Cavandar, Avella slowly regained her mind.