Paola, a curvaceous 20-year old Venetian giri, cheerful character and exuberant sensually, briskly enters the offices of a London real estate agency. She is looking for an apartment to rent for Matteo. Matteo studies at the Economic Studies University of Venice. They are in love and Matteo wants to join her in London for a "full-immersion” English course.
Moira, the fortyish owner of the agency with an ingratiating but ambiguous manner, wastes no time in transforming the business relationship into an explicit sexual advance. During their phone canversations, Paola punctually omits to tell Matteo in Venice about these events because, although she loves him, she cannot renounce what she considers to be just I'having fun".
The film recounts the erotic-amorous skirmishes that Paola's lies engender as a result af Matteo's jealousy. He has an idea of what is going on, which further enflames his jealousy, already made white-hot by the compromising photos and letters regarding Paola that have come to his notice.
His rethinking, in a different light, of several episodes of their relationship, is the straw that breaks the camel's back and convinces him to cancel his planned trip to London. Paola feels bad and reacts to the break with Mattea by accepting not only the courtship of Moira but also that of her ex-husband who, during a torrid party in London persuades her to exhibit herself along with other women in a wickled "Judgement of Paride", brandishing her nude buttocks intoxicatingly far the pleasure and amusement of everyone.
If it is true that the face can be a hypocritical mask capable of pretence and decention, then it is also true that the bottom never lies: as a noted Venetian proverb states, "Everyone is the ass they have!”. But Matteo's feelings for Paola are stronger than any resentment he might harbor, and although hit by doubtsand suspicion, he decides to join her in London.
During a turbulent confrontation, he realizes an amazing fact: even though the thought of his girl in the arms of another drives him insane with jealousy, nonetheless that very jealousy makes him desire her even more. That's why he reluctantly and ironically admits that it is better to accept Paola's betrayals for what she says they are: the most honest way of being faithful to herself while making him suffer the least. Through the lies she tells him he discovers a more exciting truth than any illusory certainty she might have concealed: extraordinarily transparent signs of the most initmate, secrets, “scandalous", unspeakable desires of Paola.
And this is why, ceasing to torture his soul uselessly in search of an elusive truth, Matteo concludes the matter in a rather surprising manner, telling her, already under tension and only apparently paradoxical: “I swear I will always lie!”