Maggie O’Connor, a psychiatric nurse in New York City, adopts her newborn niece, Cody, from her sister Jenna, a homeless heroin addict who abandoned her at Maggie’s house just before Christmas. Maggie raises Cody herself, and during her formative years, Cody exhibits symptoms of autism, though Maggie is suspicious of the diagnosis. Maggie enrolls Cody in a special-needs Catholic school in Brooklyn, where the nuns notice Cody displaying possibly telekinetic abilities.
Meanwhile, a series of child kidnappings and murders are plaguing the city, investigated by FBI Special Agent John Travis, a former seminary student. The bodies bear occult brandings, and the victims all share Cody’s birthdate and age. At her hospital, Maggie meets Cheri, a young heroin addict bearing a mysterious Luciferian tattoo, who knows Jenna. In conversation, Cheri implies that Cody is special, and urges Maggie to protect her. When Maggie and Cody stop in a church, Maggie is startled when all of the votive candles light themselves in Cody’s presence.
When Maggie returns home, she is surprised to find Jenna, now clean and sober, there with her new husband, Eric Stark, a famous self-help guru, attempting to take Cody. Maggie refuses, but they manage to covertly kidnap Cody. Maggie reports it to police, and Agent Travis takes an interest in the case. Maggie attempts to learn more about Eric’s organization, the New Dawn Foundation, by visiting one of their centers. Cheri subsequently contacts Maggie, and explains she was previously a member of New Dawn, which is actually a front for a Luciferian cult, spearheaded by Eric. She says that the cult recently began kidnapping six-year-old children and subjecting them to tests; those who failed were murdered in what Cheri describes as the “slaughter of the innocents.” Cheri claims that Cody is destined to become a saint who will lead people to God, which Eric is attempting to thwart.
A group of cult members pursue Cheri after she provides Maggie Eric’s address, and decapitate her in the subway. Maggie visits the address, located in a rundown building in Queens, and finds Eric, Jenna, and Cody there. Maggie holds Eric at gunpoint, but is chloroformed by his henchman, Stuart. She regains consciousness in the driver’s seat of car, crashing into the side of a bridge. She is helped by a mysterious stranger moments before the car falls into the river. Meanwhile, Eric attempts to force Cody to watch as he convinces a vagrant to commit suicide by lighting himself on fire. However, Cody thwarts this by blowing out the match, assuring the man he has not been forsaken. After, Eric angrily burns the man alive. Jenna, meanwhile is kept sedated with heroin.
Maggie tracks Cody, who is being cared for by a nanny and member of the cult, Dahnya, and kidnaps Cody while she is visiting an orthodontist. Another mysterious stranger, this time female, helps them catch a subway train by holding the door open. At the urging of a Jesuit priest, Maggie leaves with Cody en route to Sister Rosa’s convent in Vermont, but the cultists stalk them and manage to kidnap Cody. Maggie phones Agent Travis, who agrees to help her, tracking the cultists to a palatial estate owned by Eric. Maggie and Travis break into the home, but are assailed by cultists, who beat Travis. Maggie flees into the woods and reaches an abandoned church where the cult is preparing for a Black Mass. Meanwhile, the nuns at Sister Rosa’s convent, worried over Maggies’ failure to arrive with Cody, pray en masse for their wellbeing. Maggie stabs Eric, who then shoots her as she attempts to save Cody. Three orbs of light suddenly appear in the church as the cultists watch in terror, and Maggie’s bullet wounds mysteriously heal. Travis and other officers enter the church and shoot Eric to death, and watch as the orbs of light disperse.
Some time later, Jenna is in rehab and has asked Maggie to legally adopt Cody. While Maggie, Travis, and Cody walk to mass, another cultist stalks Cody, attempting to kill her, but stops, awestruck, as she turns to stare at him.