Father Thomas Keneally, the junior priest at Holy Martyrs, serves communion to a distraught woman in the large candlelit church. After the service, she invites him to her grim apartment where her sick son is throwing a fit. Keneally prays and the boy is calmed. It’s Keneally’s first healing. All is not well, however, when the mother bursts into the next Sunday service with the news that her boy is dead. She blames Keneally.

The police investigate but can find nothing with which to charge Keneally. But the story causes other parishioners to seek out ‘the healer’. Despite his own misgivings, he continues his ministry. All are healed of their relatively minor ailments except one soul, Michael, a teenager with terminal cancer. This is a heavy blow to Keneally’s confidence: he sets it his mission to heal the young man. Time and again, he visits to heal him. There are other dark sides to the healings. Keneally becomes wracked with self-doubt: in whose power is he healing? He suffers from disturbing dreams and visions. Rather than strengthening his faith, his healings are causing him to lose it. Not least is the pressure from his own superior. Jealous of the attention of his junior priest, Father Wiesznak also implores him to stop. But Keneally cannot deny his gift. That is until the killings begin. Keneally is suspect number one since he knows each of the victims. Should he now cease his healings in order to halt the killer’s spree? Yet there are powerful people who need his help: the city mayor’s wife is going to lose her unborn child. Keneally could help, but should he?

Demoralised, dejected and spent, Keneally decides to help just one last time. He prays over the mayor’s wife. The baby will live. Keneally returns exhausted to the dark church. He breaks down at the altar and begs God to take back his gift. But there, in the shadows, the killer is lurking. Hearing Keneally’s prayer, she leaps upon him to kill him. Fighting back, Keneally struggles with Mary, the mother of Michael – the young man he could not heal. She’s been using the blood of the healed in an attempt to heal her boy. Supernaturally possessed, Mary has powers beyond her own strength. In order to save him and Mary, Keneally prays his final miraculous prayer: that Mary be healed of her murderous demons.