Mystell is a resident of Killorn Keep, responsible for the inner security. When she met the Avatar for the first time in Ultima Underworld II, she tested the hero on knowledge and loyalty to the Guardian. Not knowing the Avatar's identity, Mystell revealed that she was the ears and eyes of the Guardian in the keep, trying to root out any traitors, voicing her suspicion about Altara. When the Avatar later returned to Killorn Keep, it turned out that Mors Gotha had practically relieved her of her post, making her doubt if she had been loyal enough to the Guardian.