This was shown on the MGM channel early this morning and I hadn't seen it since its' first release so I watched it again. Hard to believe that John Schlesinger would be able to tackle a horror film and do it well but he did.
Based on the novel The Religion
by Nicholas Conde, the story involves a widower psychologist played by Martin Sheen ~ the reason for his being a widower is shown in graphic detail
~ and he gets involved with the doings of a ritual cult in New York, as does his innocent son, whose interest in the cult makes him a target for their evil doings.
Quite gory, very scary and that ending: YIKES!