A gutter press contact informs corrupt Commissioner Belli (Franco Nero) that respected lawyer Fontana (Adolfo Celi) wants him to make trouble for English model Sandy Bronson (Delia Boccardo) who is engaged to his son Mino (Maurizio Bonuglia). Fontana is also perturbed about a business deal his son wants to enter into with recording studio owner Romani (Marino Mase). After roughing up Sandy, Belli pays a call on Romani only to discover that the man has been murdered. When Belli's colleague Baldo (Renzo Palmer) questions the doorman of Romani's apartment building, Belli recognizes his description of a female visitor as that of Sandy. They also discover the seemingly important clue of a photograph of a naked woman whose face is obscured because the corner of the photo is torn off. When Belli confronts Sandy, she reveals that she had been to bed with Romani and that Mino had found out. When Baldo arrives to question Sandy, Belli agrees to not reveal that she had keys to Romani's apartment if she does not mention that he has ever come to visit her. Naturally, Fontana is not too happy that his son might become a potential suspect in Romani's murder. Mino's doting stepmother Vera (Florinda Bolkan) was all for Mino investing with Romani, so Belli questions her (she even strips off to reveal that she is not the woman in the photograph found in Romani's apartment). Sandy swears that she is not the woman in the photo (although she does not prove it in the same manner) but claims that Mino's photographer friend Claude (Roberto Bisacco) was looking for a negative and questioned her since she had been to bed with Romani. Belli roughs up Claude, but does not find the negative so he pays a visit to French singer Emmanuelle (Susanna Martinkova) who Mino introduced to Romani. Belli picks up quickly on her drug problem, but that's a dead end since her doctor supplier (also introduced by Mino) met with a sudden fatal accident the week before. Belli plays Russian Roulette with Sandy in his car (denting and dinging several other cars on the road along the way) and she admits that she was the girl in the photo and that she and Mino went looking for it and both discovered Romani dead. She also admits that she does not want to marry Mino; rather, she wanted Fontana to buy her off so she could provide for her layabout boyfriend back in England. If blackmail was not the motive for Romani's death, then why was he killed?