One hot summer night, best friends Lourdes, Fernanda, Ana, Perla, and Pauline hold a séance. It's all fun and games at first, but their tipsy laughter turns to terror when the flames burn straight through their prayer candles and Fernanda starts crawling toward her friends and chanting in Nahuatl, the language of their Aztec ancestors.

Over the next few weeks, shy, modest Fernanda starts acting strangely-smearing herself in black makeup, shredding her hands on rose thorns, sucking sin out of the mouths of the guilty. The local priest is convinced it's a demon, but Lourdes begins to suspect it's something else-something far more ancient and powerful.

As Father Moreno's obsession with Fernanda grows, Lourdes enlists the help of her "bruja Craft crew" and a professor, Dr. Camacho, to understand what is happening to her friend in this unholy tale of possession-gone-right.