"I wanted everyone to see how rotten they were!"
- Agatha about the town council
Agatha "Aggie" Prenderghast is the central antagonist of ParaNorman. She is the legendary witch of Blithe Hollow, Massachusetts, who was hanged in the year 1712. However, she was truly a young girl whose only ability was that she could see and speak to the dead. She cursed the seven judges who convicted her to rise from the grave as the living dead so that the living would torment them.
Agatha lived with here mother in the small town of Blithe Hollow, Massachusetts. Like her distant relatives, Mr. Prenderghast and Norman Babcock, Agatha could see and communicate with ghosts. The ghosts of the town started talking to her at some point, prompting her to talk back to them. When the other villagers in the town found out about this, they suspected she was a witch. She was later arrested and put on trial. Her six main accusers and the local judge, Judge Hopkins, found her guilty of witchcraft and sentenced her to hanging. However, after her execution, her ghost cursed Hopkins and her accusers to die and rise from their graves as the living dead. It was only until death that Agatha's accusers realized their mistakes. To keep the curse from happening, other members of Agatha's family who also had her ability would read her mother's bedtime stories to her on the anniversary of her death, calming down her ghost.
Agatha's ghost awoke on the 300th anniversary of her death when Norman Babcock, who was given the responsibility of keeping her ghost at bay, failed to read the book at the correct spot she was buried. Taking the form of a storm resembling a witch, Agatha summons the cursed seven as zombies. Norman attempts to get information on where Agatha was buried from his fellow classmate, Salma, who informs him that people found guilty of witchcraft were buried in unmarked graves, but also that Agatha was tried in the Town Hall, so there may be a record on her execution and burial there. The zombies follow Norman and his friends into Blithe Hollow, where they are attacked by the local townspeople. Norman and his friends break into the Town Hall and search for Agatha's records, but are left with no answers. The zombies break into the Town Hall as well and chase Norman to the top of the building, where the witch storm appears. Norman climbs the tower and tries to read the book to her, but Agatha is too consumed with rage to listen to it and strikes him down with lightning.
Norman has a vision of Agatha's trial while he is unconscious, and wakes up just as the zombies confront him and reveal they wanted to talk to him so he would read the book to Agatha and send them all back to the grave. Norman is initially reluctant to help them after learning of what they did to Agatha, but agrees to. However, since the book is destroyed, Norman decides to confront her and end the curse permanently. Norman convinces the mob to stop their attack, enraging Agatha's ghost, who attacks the town. Judge Hopkins directs Norman and his family to Agatha's grave. Agatha separates Norman from his family, forcing him to confront her by himself. Agatha attacks him in an attempt to get him to leave, but he stands his ground against her assault and tries to reach through to her. Agatha' ghost then opts to try and leave, but Norman grabs her hand and she reverts to her normal self before her death. Norman and Agatha have a quiet conversation, and Norman manages to convince Agatha to remember to good people in her life, and telling her he doesn't believe she is a witch. Agatha manages to find a measure of peace and passes onto the afterlife, along with the zombies.
- Agatha was hanged in the year 1712 at the age of 11, meaning she was born either on 1700 or 1701.
- Agatha is essentially what Norman would have become if he had become bitter and cold from the treatment he received from the town.
- Agatha's name is revealed earlier in the movie when one of Norman's classmates, Salma, reads about the trial and execution on her laptop and her full name is briefly shown.