Pick-Up Girls (1981)

Original title: La chica de las bragas transparentes

Private eye Al Crosby is paid by millionaire Harry Feldman to take his place at a meeting with Emilio, a gangster. He is drugged and photographed in compromising positions by two hookers, Suzy and Bijou, then he is nearly killed by Mrs. Feldman. Al tries to blackmail Mrs. Feldman, and he is beaten up by three women and forced to tell of Harry's whereabouts, leading to Harry's murder. Al enlists the help of Harry's mistress, Coco, plus Suzy and Bijou whom Al gets out of prison, to expose Mrs Feldman as having inherited money by devious ways and being a brothel owner.