Fifteen years after the harrowing events that led to the death of a young girl and a priest, Lieutenant Kinderman is confronted with a series of gruesome murders that mirror the modus operandi of the Gemini Killer, who was executed the same day of the exorcism. These brutal killings coincide with the death anniversary of his friend, Father Karras, and the senseless violence shakes him to his core. The murders are particularly disturbing as they bear the same hallmarks of the Gemini's—signatures that were never released to the public—suggesting the impossible scenario of a copycat who knows intricate, unrevealed details, or something more supernatural at play.

Kinderman delves deeper into the investigation with the help of his close friend, Father Dyer, whose faith offers a sharp contrast to the lieutenant's pragmatism. Unexplained events intensify as Kinderman connects the inexplicable acts to the psychiatric unit of a local hospital, where an enigmatic patient is held in a secure ward—a man with no identity who exhibits an intimate understanding of the original Gemini killings and a connection to the long-dead Father Karras. This patient's unsettling presence and knowledge thrust Kinderman into a nightmarish quest for truth that challenges both his rationality and his most deeply held beliefs.