REFLECTION OF FEAR (1972)
Directed by William Fraker
Starring Robert Shaw and Sally Kellerman
Atmospheric murder mystery makes effective use of old-fashioned dolls and the ambience of a dark and gloomy mansion. A teenager (Sondra Locke) starts acting strange when her divorced Dad (Shaw) shows up to meet Mom's new fiancée and someone on the grounds starts committing murders. The twist ending, which has been imitated many times since, is pretty satisfying. Heavy duty horror hounds should already know which franchise would later borrow the twist end to kick off their own film series, but in case they don't, it's the "Sleepaway Camp" series.
Recommended, if you're lucky enough to find it somewhere.