Father Tomas Ortega is the new face of the Catholic Church: progressive, ambitious and compassionate. He runs a small, but loyal, parish in the suburbs of Chicago. Father Marcus Keane is a modern-day Templar Knight, an orphan raised since childhood by the Vatican to wage war against its enemies. Marcus is everything Tomas is not: relentless, abrasive and utterly consumed by his mission – and he constantly butts heads with his adversary within the church, Father Bennett.
Angela Rance suspects a demonic presence has entered her home, and enlists the help of Father Tomas Ortega, who calls on experienced exorcist Father Marcus Keane.
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. 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.
With no sign of their missing daughter, the Rance family begins to disintegrate; Marcus looks to Mother Bernadette for help with the latest problem; news of Casey's possession goes public and Father Bennett continues his probe into Tattersal.
As Marcus, Tomas and Mother Bernadette race against time to defeat the demon, the Rance family finds itself drawn into the conflict. With the Pope's visit only days away, the church's enemies take aggressive new moves. Angela confronts a familiar face from her past, and Kat considers a new future.
On the eve of Pope Sebastian's visit to Chicago, Marcus and his companions race to avert a potential tragedy. Tomas is offered a life-changing opportunity, but will the sins of the past endanger his future within the church? Meanwhile, as the Rance family attempts to recover from their most recent ordeal, a new problem threatens to tear them apart.
Season Finale. Everything has led to this moment. Forty years ago, the demon was denied its prize. Now it will stop at nothing to destroy Angela Rance and her family. Their only hope lies in two men: Marcus and Tomas. But with the enemies of the church mobilizing against Pope Sebastian, time is running out for everyone.