Set fifteen years after the original film, The Exorcist III centers around the philosophical Lieutenant William F. Kinderman who is investigating a baffling series of murders around Georgetown that all contain the hallmarks of The Gemini, a deceased serial killer. It eventually leads him to a catatonic patient in a psychiatric hospital who has recently started to speak, claiming he is the The Gemini and detailing the murders, but bears a striking resemblance to Father Damien Karras.
Mourning the accidental death of his wife and having just moved to New York with his young son, laconic police psychologist Cal Jamison (Martin Sheen) is reluctantly drawn into a series of grisly, ritualistic murders involving the immolation of two youths.
Detective Emily Eden is a tough New York City cop forced to go undercover to solve a puzzling murder. Her search for the truth takes her into a secret world of unwritten law and unspoken power, a world where the only way out is deeper in!