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

While 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. As the storm of the century descends upon Chicago, Father Tomas and Marcus engage the demon in spiritual warfare. But the demon is ready and waiting with a few secrets of its own. Meanwhile, the demon's manipulations slowly begin to drive a wedge between members of the Rance family. Loyalties will be tested and lives will be forever changed.

The Rance family is engulfed in a firestorm of publicity after the media learns about the possession of Casey Rance. As Casey's story continues to make national headlines, Father Tomas finds himself unexpectedly thrust into the public spotlight. Meanwhile, Father Bennett attends a papal planning gala at Maria Walters' mansion, where members of high society gather to discuss the presence of angels in everyday life, and Marcus’ search for answers leads him into the terrifying underbelly of the city.