Marnie Stonebrook is a major character in the fourth season. She is portrayed by Fiona Shaw. She was a very powerful medium who served as a leader of a Wiccan coven at the Moon Goddess Emporium. She was the main antagonist for Season 4.
A mousey and quiet woman, Marnie was the owner of the Moon Goddess Emporium shop. Marnie always had a thirst for power and hated humans for they treated her as if she was weird when she believes she did not choose what she is. One day, during one of her groups practices Marnie became possessed by the powerful, yet deceased, witch Antonia Gavilán who used Marnie as a way to curse and kill all vampires by having them meet the sun. Throughout the fourth season, Antonia made various attempts to kill the vampires but one of the attempts ended in the bloodshed of many humans, causing Antonia to feel remorse. Marnie's former student, Jesus, believes she is under possession and is being held hostage by Antonia but it is revealed that Marnie herself is the one in charge. Antonia wants out of their partnership after Marnie kills Casey and Antonia sees that she is now evil. But Marnie isn't ready to give up quite yet. Marnie was the main antagonist of the fourth season.