Roz and Susie confront Sabrina about being a witch and she tells them everything.

Madam Satan sacrifices a student at the Hanging Tree to conjure the Greendale Thirteen, witches sacrificed by the coven and hung by mortals centuries earlier. The Thirteen summon the Red Angel of Death and send Ambrose to warn everyone.

Father Blackwood orders all witches to the Academy for their safety. To protect the mortals, the Spellmans conjure a tornado for them to congregate in the storm shelter at Baxter High. The Spellmans cast a protection spell on Baxter High, but Ambrose and Zelda are summoned to the Academy.

Madam Satan takes Sabrina to the woods and convinces her to sign the Book of the Beast to gain the power to defeat them. Sabrina unleashes Hellfire on the Hanging Tree and the Thirteen, burning their souls and banishing the Red Angel of Death.

She also seemingly chooses the witch side, visiting Harvey after he and Nick protected his house, to tell him that they can't back together. Now that she signed her name away she is worried about her friends and him and wants to stay away.

During the events, Lady Blackwood dies while giving birth and Zelda lies to Father Blackwood, claiming the larger twin consumed the other when in reality the first-born twin was a girl. She is worried what he would do if his heir wasn't male so she and seemingly Prudence keep it a secret.

Zelda expects to raise the child with Hilda but Hilda plans to move out. She has a growing relationship with the guy who owns the bookstore, who is revealed to be some kind of supernatural being without her knowledge. 

Later, Madam Satan reveals her plan of becoming the Dark Lord's Queen to Hawthorne, before killing him and her familiar.

The finale wraps up with Sabrina's friends not knowing what happened to her and it is revealed that she is now close with The Weird Sisters, possibly more evil than before, winking to a shocked Nick as she strolls by.