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Movies like The Keeper (1976)

The Keeper of Underwood Asylum has the mental patients of the wealthiest families in British Columbia. The rest of the family members have been dying under mysterious circumstances, so Biggs hires private investigator Richard Driver, who puts his assistant, Maybelline, in the asylum pretending she is his cousin and that they came from a family where the parents were all first cousins to each other and they decided to keep their love platonic for genetic reasons. Then he tries to get Inspector Clarke to check him in as a narcoleptic who didn't wake up with his body. They all know what the keeper has been doing, but it is a matter of proving it, and avoiding the hypnotized Biggs twins and Danny, who he is able to keep catatonic with his machine. Inspector Clarke gives driver a lot of trouble, and the kid giving shoe shines looks down on everybody, knowing more.