A beautiful, wealthy young heiress (Adriana La Russa) is tricked by her no-good, blackmailer lover (Nino Castelnuevo) into going to a brothel to make love. After she is caught up in a police raid her lover arranges, her family, to save face, decides to have her put in a mental institution. She gets out, and pretending to be crazy (like a very sexy female Hamlet), proceeds to get revenge on everybody including her lover, older sister, brother-in-law, and not least of all, her father (Rosanno Brazzi, who also directed).
This is basically a late 60's Italian gialli. It is not nearly as violent as the films that would later follow Dario Argento's "Bird with Crystal Plumage". It's perhaps more in the the spirit of the "Diabolique"/"Dolce Vita"-type gialli of the late 60's, typified by the films Umberto Lenzi made with Carroll Baker, where jaded wealthy jet-set types scheme against each other. This movie is not as stylized as the Lenzi/Baker films (the direction is actually a little flat), but it is has a good script and it is very well acted, especially by LaRussa. LaRussa had also appeared in Lucio Fulci's "Beatrice Cenci", another film about twisted family relations. She is great and very sexy here as she seduces her hapless brother-in-law, frames one character for the murder of another, and drives yet another to an early death. LaRussa kind of reminded of the late Soledad Miranda in films like "She Killed in Ecstasy". There's little doubt for her victims that beneath her seeming madness lies a scheming malevolence, but they simply can't resist her (much like a male praying mantis can't resist the female that is going to tear him apart and devour him). LaRussa may not quite be as sexy as Soledad Miranda (but who the hell he is?); however, she may very well be a better actress.
This is not one of the better directed gialli, but it has a strong plot and is very well acted, and it certainly deserves to be more widely seen.