The Believers (1987)
Nothing Can Stop Them. No One Can Help You. They Know Who You Are.
While investigating a series of brutal murders, a psychiatrist for the NYPD uncovers and becomes interested in a dark religious cult, the members of which (the "Believers") use children as human sacrifices. But the psychiatrist soon realizes he must extricate himself from the grip of the Believers and its rituals -- before his own son becomes the next to be sacrificed.