Mattie has apparently been active in Kingsbridge for years, using her treatments to do everything from cure ailments to aid in pregnancies. Her use of herbs and other treatments that conflict with what priery physician Brother Joseph believes are best causes him to resent her greatly, and he ultimately accuses her of witchcraft, much to the contention of Caris and many other people of Kingsbridge who have benefitted from her treatments. Unfortunately, the presence of a "mark of the devil" in the form of a physical deformity on her breast condemns her. Though the bridge where she is to be hanged collapses under the combined weight of too many people, she ultimately dies anyway, leaving Caris distraught but also forcing her to continue where her mentor and friend left off.