The Changeling (1980) directed by Peter Medak
New York composer John Russell (George C. Scott) loses his wife and daughter in a horrible accident which he witnesses. Months later, he moves to Seattle to teach at a university, more so to get away from bad memories. He winds up renting a house from the local historical society. It's an old house with a grand music room, seemingly perfect if a little too large for one man to live in. He starts hearing noises that have no logical explanation. The noises lead him to a hidden room where a young boy was killed. Russell is terrified and fascinated by the mystery. He calls in help from the psychiatry department of the university. In an unnerving seance, a medium makes contact with the ghost who provides some details that suggest the boy's true identity. The secret is not one that everyone wants to keep.The movie is a quintessential slow-burn horror/mystery. The story moves at a slow pace, providing a lot of atmospheric music and odd scenes that gives the house a daunting and melancholic tone. The people from the historical society provide a slow but steady trickle of information (doing research before the age of the internet was a slow process). Scott gives the right level of frustration and determination to his character, making him very sympathetic. The gore is minimal but the depiction of the boy's death is very disturbing. The movie delivers on the chills and provides a satisfying ending.
Highly recommended--easily in the top ten haunted house movies ever made.