Sister of Darkness: The Nicci Chronicles Series Novels

Heart of Black Ice (Sister of Darkness: The Nicci Chronicles 4) by Terry Goodkind
Siege of Stone (Sister of Darkness: The Nicci Chronicles 3) by Terry Goodkind
Shroud of Eternity (Sister of Darkness: The Nicci Chronicles 2) by Terry Goodkind
Death's Mistress (Sister of Darkness: The Nicci Chronicles 1) by Terry Goodkind