Luigi (Ron Nummi), who is engaged to a rich bourgeois Cinzia (Simona Borioni) is trying to conclude a billionaire contract, to sell to a Japanese businessman a large land for construction programs. He meets his lovely cousin (uncle’s daughter) Sonia (Vittoria Belvedere) at the cremation of their grandmother. Six months later Sonia moves in and enters his life and gradually succeeds in seducing him. She upsets his life: Cinzia is immediately jealous but he can not resist the seductress. She is the cause of breaking the engagement with his fiancée. She lets him participate in threesomes and partner swaps, seduces his boss and ruins his career. Sonia not only decided coldly to annihilate him, but soon manifests all her own wickedness. From her secret diary, Luigi discovers strange confessions; then he finds with horror the body of Francesca (tortured); he learns that his beautiful cousin has murdered her parents. Despite the passion and the sex that make him a prisoner, that the lover is a dangerous schizophrenic and without any hope whatsoever. But because of her concern, the wife of his boss still saves him.