Naked Girl Killed in the Park (1972) on Netflix

Plot summary

Chris Buyer, an insurance company's best investigator, is sent to look into the family of Johan Wallenberger, a wealthy financier killed in an amusement park's Tunnel of Horrors in Madrid. Wallenberger had taken out a million dollar life insurance policy on the day he died. Chris approaches the dead man's daughter Catherine at a reception; she has been blackmailed through phone calls about her father's murder and believes he is behind them. She lets him drive her home and agrees to a date. Through her he is invited to the family's country house, where the widowed matriarch Magda has ordered her husband's study left off limits, and where Catherine's sister Barbara, the stableman Günther, the maid Sybil and the butler Bruno all live.