Georgetown, Washington D.C. Seventeen long years after the execution of the Gemini Killer and the fateful night of pure terror in The Exorcist (1973), a spate of grisly killings bearing the trademark of the mass murderer terrorizes the district. And as the death toll keeps rising, skeptical police officer Lieutenant William F. Kinderman is still obsessed with solving the baffling case. In the meantime, in the city's high-security psychiatric institution, a cryptic inmate bearing an uncanny resemblance to the late Father Damien Karras emerges from his deep catatonic state, claiming he has all the answers Kinderman needs. But who is the mysterious Patient X? Does the same unholy force that tormented Regan MacNeil have something to do with the brutal demonic murders?