Guido Quiller, Adriano Celentano, is the inventor and main patent proprietor of an almost indestructible armored glass used to secure jewelry shop windows. This breakthrough threatens the profits of powerful insurers, notably the La Suisse Assurance in Geneva, who see their lucrative niche shrinking and plot to seize the patent and wipe it out.
Petula, Olga Karlatos, is the other patent holder and Guido’s wife. She makes divorce a condition for transferring all exclusive rights to her, enabling her to sell them to the insurer and reap a princely compensation.
On the day Guido reveals he will lose all his money, his younger lover Maggie, Ania Pieroni, walks out, revealing her interest was financial as much as romantic. As he races after Maggie on a defective Vespa to recover her handbag, Guido attracts the attention of Tilli, Eleonora Giorgi, a subway pickpocket with a fascination for horoscopes and Arsene Lupin, and her brother Momo, Memo Dittongo, a bumbling counterfeiter. Their grandfather, Gianni Zullo, had earlier tried to break into a jewelry shop but was thwarted by the Quiller glass and arrested.
When Guido crashes into a fountain, he emerges with laryngitis, rendering him temporarily mute and unable to identify himself. Waking, he meets Tilli and finds himself drawn to her, even though she and her friends view him as a scoundrel because of his invention. He confides in his faithful butler, Benny, John Sharp, about his growing affection and the knot in his identity, and Benny suggests Guido should become a thief himself. Cleverly, Guido borrows Benny’s name publicly to stay anonymous and then bails Tilli’s grandfather out of prison, becoming a skilled master thief and gradually winning Tilli’s affection.
To win her completely, Guido stages a break-in at his own villa, presents her with a ring, and plans to reveal his true identity. But a call to the police by Leo, Gino Santercole, Guido’s rival for Tilli’s heart, exposes him, and Tilli leaves in a rage. The next day, Guido sets a trap for Tilli at her usual hangout and whisks her to Geneva, to the office of the Suisse Assurance, where he demonstrates his true intentions by surrendering his entire fortune to his ex-wife in exchange for the divorce.
Petula notices the loss and demands it back at gunpoint, but Guido, Tilli and Benny drive off with a twist: Guido reveals that he has retained the real money while surrendering to Petula the flawed dud money that Momo has produced. The bank and the law may loom over them, yet the trio drives onward, leaving the door open for a future that blends risk, romance, and a clever bit of fortune, all while the unlikely couple navigates trust, deception, and a way to beat the system using wit, charm, and a little audacity.
