In the crypt of the remote castle of the Aguilars lies the recently-deceased body of Maria. Her husband Antonio is a jealous bully, his mute brother Ignazio is in a wheelchair peeping on his caretaker Sol, a novice. Also present are Miria, the couple's virginal daughter, and Isidro, a factotum who fears Satan's power. A frequent visitor is Juan Suarez, a doctor who wants Miria in a sanatorium for a month. She doesn't want to go. Isidro tries to exorcize the castle's evil spirits. Bodies pile up. Is Miria's mother truly dead, and who is Satan's tool?