Three weeks after Melissa, the sixteen-year-old daughter of Barbara and Mark Harding was abducted, no demands for ransom have been received. Guided by the retired U.S. Marshall John Bernstein and husband of her good friend Susan, Barbara is put in touch with a psychic named Sterling. Though he is currently busy with another case of an abducted child, Sterling secretly gives Barbara a powerful crystal that soon protects her from a dark presence in Melissa's bedroom. When a young girl named Jessica Taylor tries to steal the crystal, Barbara begins to realize that her family is caught in a web of the terrible evil that stretches back 500 years.

Unknown to Barbara, Jessica's older sister Heather is trying to thwart the very evil that threatens two families. Guided by a 500-year-old spirit named Tobias, the girls' father, Martin Taylor, has kidnapped Melissa and dug up from a grave an ancient jeweled dagger and a book of powerful magical spells, which he will use to sacrifice Melissa during the upcoming night of a "blood moon." Hoping to prevent her father from becoming a murderer, Heather steals the "Jillian Dagger" and hides it in a cave, where she is almost captured by the disembodied sorcerer Tobias.

Barbara meets Heather when she discovers the girl hiding in the Bishops' parked boat and is told the story of the curse on their two families: 500 years earlier, the wizard Tobias had set in motion a spell of black magic that required a mother to voluntarily give up her innocent daughter as a sacrifice granting Tobias a form of near-immortality. Now, bound by the curse, a descendant of the Taylor family must sacrifice an innocent child of the Bishops using the Jillian Dagger for Tobias to regain physical existence. Sterling appears and resolves to stay with the Bishops until he can figure out how to combat the evil wizard and prevent the sacrifice of the Bishops' daughter.

Heather is captured by her stepmother Ilene and forced to take her father and Ilene to the cave where she hid the Dagger. Tobias manifests, however, and psychically devours Ilene's mind. Escaping, Heather runs home, where she discovers that her older brother Tommy has burned down the house while trying to evoke a spell with the book of magic, killing four of their siblings, including Jessica, and landing him in jail. Heather collapses and is taken to the hospital. Martin abducts Melissa's younger sister Rachel from John Bernstein, whose mind Tobias cannibalizes.

Sterling calls in the occult paleontologist Professor Etheridge and his Apache shaman friend Rothay to help him combat the forces of evil, and the professor identifies the book of magic as a very powerful and dangerous book of spells. They enlist the aid of Shakira Spell Binder, who takes them to the secret lair of Stannis, a powerful magician. While Stannis is defusing the book, Rothay is killed, and the remaining allies begin preparing for the final duel with Tobias.

While visiting the ruins of his house, Martin Taylor is killed by police, and Tobias springs Tommy from jail to help him in the sacrifice of the innocents. Stannis, Shakira, and Barbara, guided by Sterling, confront Tobias and Tommy at the site of the sacrifice. Although Shakira is killed, Barbara relies upon her mother's love and the power of the Mother's Regret crystal to rescue her daughters and kill Tobias.

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