PRETTY POISON (1968)
Starring Anthony Perkins and Tuesday Weld
This unjustly forgotten, highly disturbing film deserves a serious revival. It's incredibly hard to find. I caught it on TV way back in the '70s. It occasionally shows up as a video bootleg. Not really a horror film so much as a thriller, but Perkins naturally makes it feel like one.
Perkins plays a disturbed arsonist who gets into a sick relationship with high school student Weld, who controls him do anything—including murder. Telling her he's a secret agent, she seems to dig the fantasy. It's only when an attempt at petty crime turns into murder that it becomes clear that she's more dangerous even than he is. It's chilling and has enjoyed cult film status for three decades, even turning up in books on cult cinema. Many consider this to be Weld's finest performance.
The film was released by 20th Century Fox, a studio known for burying its long-lost cult gems.