Something is wrong in the Rance household. Angela Rance suspects demonic possession and enlists the help of two priests: the progressive, but naive Father Tomas Ortega and the broken holy warrior, Father Marcus Keane. Together they will be drawn into a nightmare beyond imagination.

When Bishop Egan denies Tomas permission to perform the exorcism on Angela's daughter, Father Marcus breaks out of Saint Aquinas and joins forces with Tomas, though he urges him to get his ex, Jessica, out of his life and heart. The Rance family's relationship with the demon deepens and when Marcus catches Angela stealing holy water, he instructs her on how to use it. On Chicago's south side, a series of bizarre ritual killings begin taking place.

Kat struggles to confront the realization that her friend, Julia, is dead. Shopping for a dress to wear to Julia’s memorial service, Casey is given a sexy, expensive and slightly inappropriate dress by a salesman at the store. Seeking permission to conduct an exorcism, Marcus and Tomas take footage from the Rance home to papal emissaries, only to be met with shocking news that will change Marcus' life forever

Angela grows restless as her daughter's condition continues to deteriorate, and the demon turns its attention toward innocent victims. While Father Tomas is paid a visit by a familiar face from his past, Marcus journeys to an unexpected destination and receives guidance from a most unlikely source. With time quickly running out, the two priests must decide whether to defy the church by performing an unsanctioned exorcism.

The exorcism begins; Father Tomas and Father Marcus engage the demon in spiritual welfare, but the demon has a few secrets of its own, as the manipulations begin to drive a wedge between the Rance family.