Scenic prelude The famous Neapolitan actress Silvia Lombardi was abruptly torn from her sleep. A masked stranger entered her room, kissed her passionately and wanted to carry her away. But this scene lasted only a short time: frightened by noise, the man jumped out of the window. Silvia screams for help.
Act 1 In the meantime, all of Naples has heard about this incident. Even in the fashion salon "La bella di Napoli" the mannequins gossip about it. Only the Parisian Louise cannot understand the excitement about a simple kiss. The fashion designer and salon owner Andrea Coclé resents this talk. Left alone, he makes a passionate declaration of love to a tailor's dummy modeled on Silvia's figure - he is madly in love with the actress. Silvia, on the other hand, is particularly enamored of Andrea's fashionable creations and pays a visit to his atelier. Their flirtation is interrupted by the sensational reporter Sam Borzalino, who is writing an article about the break-in at Silvia's villa and wants to interview her. Andrea compliments him out and lets Silvia try on a new dress. The next troublemaker is Caretto, the police minister, who has meanwhile taken charge of the burglary. He takes a closer look at Andrea, who finally confesses to having been in the garden of Silvia's villa at the time of the alleged crime. He had offered her a serenade, which he had not sung with his voice, but with his soul - a silent serenade. This suspicious behavior leads to Andrea being arrested for attempted kidnapping of Silvia and threatened with the death penalty.
While continuing his investigation at the fashion salon, Sam meets Louise. The two fall in love with each other.
Silvia pays a visit to her fiancé, the Neapolitan Prime Minister Benedetto Lugarini, and tries to persuade him to pardon Andrea. However, when he learns that the crime was a kiss, he refuses. In any case, he is furious that the newspapers are full of reports about the break-in at Silvia's, but not a word is said about the failed bombing attempt that was made on him the previous night. He asks Caretto to give priority to the search for "his" criminal over Silvia's case.
Caretto learns that the King of Naples wants to pardon Lugarini's assassin on the occasion of his birthday. With this information, the police minister wants to get Andrea Coclé to confess to both crimes - so he can claim to have solved the case and at the same time save Andrea from death. But it is only after a reenactment of a kiss with Silvia, in which she recognizes the fashion designer without any doubt as the "guilty party," that Andrea agrees to the plan.
Act 2 At the trial to determine Andrea's guilt, all the characters meet: Silvia, Andrea, Lugarini, Caretto, Louise and Sam.
In order to be credible as a bomber, Andrea shouts various slogans in the courtroom, with which he attracts not only the hatred of Lugarini, but the enthusiasm of the people of Naples who are also attending the trial. In fact, the fashion designer is found guilty and sentenced to death. His last wish is to have dinner with Silvia, which she grants him. As a result, she gets into a heated argument with the jealous Lugarini and the two break off their engagement.
Andrea and Silvia have dinner together and finally confess their love to each other. However, the romance is interrupted by Caretto, who has to give Andrea some disastrous news: The King of Naples has suddenly died without having signed the pardon - Andrea now actually faces the death penalty. There is no hope of another pardon, if only because none other than Lugarini has declared himself the new regent of Naples.
The people, however, have not forgotten Andrea's appearance in the courtroom: Through a revolution, the hated Lugarini is deposed and the alleged assassin Andrea is miraculously declared the new regent of Naples. Although the fashion designer escapes death, he is plagued by a guilty conscience - after all, he did not commit either of the two crimes he was accused of.
Fortunately, the real bomber comes to him and insists on his right to be appointed prime minister for the planned crime. So far, so good! But what if the real burglar also makes himself known in Silvia's villa and claims a right to the actress with passionate kisses?
Fortunately, it turns out that Silvia is sleepwalking and has only dreamed the kiss as well as the attempted kidnapping. Andrea is overjoyed and has nothing more to fear.