Act I

The first act takes place in the entrance hall of a fashionable beach hotel in Sorrento. Baron Mörsburg is seated at one table while Adelheid and her young man Ferdinand are seated at another. The waiter Emilio and the landlord inform the Baron of the young couple's planned wedding in the hotel that evening. Ferdinand sings that he now will leave his bachelor days behind and in a duet he asks Adelheid which colour she prefers. He loves red roses, but the girl prefers blue forget-me-nots. The character of the duet has nothing corresponding to it in earlier Strauss operettas. The Baron receives a telegram from his friend Princess Ninetta Campocasso, asking him to reserve a room at the hotel.

Ninetta is the widow of an Italian prince, but is originally from Russia. When she arrives, she is dressed as a young man, Carlino. The Baron, of course, recognizes her, but the other guests see her as a man. In a song she introduces herself as a guide. Her good looks immediately arouse the interest of female guests. At that moment Adelheid and Ferdinand's parents appear. Ferdinand's mother, Anastasia Knapp, is a widow. Adelheid's father, Prosper Möbius, is an Austrian widower who owns a silk factory. Anastasia and Prosper, in their youth, were once in love with each other, but they were unfortunately not allowed to marry. In a duet they both praise Italy, she for the culture, he for its food.

Now two other guests appear, Cassim Pascha and Rustan, his servant. They have travelled with an Italian circus, in which Cassim was a hypnotist and also had the task of holding a trapeze artiste's line with his strong teeth. Before that he was an Egyptian Minister of Finance. Baron Mörsburg recognizes him soon as an old friend, a Russian noble named Tatischeff. He is now on his way to St Petersburg in order to look after his estate. As he is dressed in a caftan and fez, the guests at the hotel call him 'the Turk'. He now sings about his home country, where blood and vodka flow, but also about his diplomacy which is so sophisticated that nobody can discover his intentions.

In the Finale I the wedding ceremony starts. To perform the marriage, the German consul of Naples, von Rübke, arrives at the hotel. He is not happy about the marriage, as he himself in the previous year, had proposed to Adelheid but been rejected. Among the identity papers he finds that Ferdinand's mother, Anastasia Knapp, is called Anastasia Möbius. Prosper then declares that, as a surprise and present for the young couple, he and Anastasia have married in Nice the day before. At once Consul Rübke establishes the fact that Ferdinand and Adelheid are stepbrother and stepsister, and thus are not allowed to marry. The only way out of the problem is for the parents to divorce, but to divorce legally there are only two valid reasons, infidelity or bodily assault. The couple, however, do not want to be divorced under false pretences and admit to something that they have not done.

Act II

The second act takes place on the hotel's roof terrace. A steaming and smoking Mount Vesuvius can be seen in the background. Ferdinand is drawing a picture at his table, when a young girl out of sheer curiosity takes a look at it and recognizes Princess Ninetta's face. Ferdinand sings in embarrassment a song about the artist's delight to make a drawing of a beautiful woman.

Among the guests Emilio gossips about a mysterious man, who has robbed and killed some tourists on the path to Vesuvius. Consul Rübke, the English Lord Plato and Baron Mörsburg are on the terrace when Ninetta appears, now as a pretty young lady.

Consul Rübke and the others notice Ninetta. Lord Plato is in a very special situation. He has made a bet and is not allowed to say anything at all. He is informed of Ninetta's talent for disguising herself, but simply says 'Hum'.

Cassim Pascha joins the company. He too is charmed by Ninetta and teaches her how to hypnotize. He also asks Ninetta to go with him on a tour to the volcano. This makes Emilio suspect that Cassim is the robber Fra Diavolo. After a short time, however, Ninetta appears again as a boy, and (only to the audience) sings about the tragedy of being born a girl. Ninetta immediately becomes the object of Anastasia's admiration. Cassim appears and in spite of his earlier declarations that he does not like women at all, he takes a walk to the beach looking for Ninetta, singing about a lovely pure young girl. This was not sung at the first performances of the operetta, where, instead, Anastasia sang 'Er soll mich verschmäh'n'.

In Finale II, when Cassim returns from the beach without the lady, but holding her walking stick, the hotel guests are now convinced that he is the robber. The fact alone that he is a Turk makes him a suspect. Everyone must see that he has the evil eye. They all demand that Cassim should leave the hotel. Cassim then declares that he has bought the whole hotel and is now the true owner of it. He also offers to make Carlino the manager. A judge and policemen are called, and the guests accuse Cassim of the murder of Ninetta, the guide, Carlino and the Princess Campocasso.

Act III

The third act opens in the hotel's banqueting rooms, where a tarantella opens the ball. Cassim burst out singing a waltz about polygamy and a children's ballet follows . The Pizzicato Polka (Neue Pizzicato Polka, Op.449) was composed by Strauss in the spring of 1892, long before finishing the operetta.

Before all the guests Baron Mörsburg declares that the charming Ninetta, to whom all the men were attracted, is a man, and the handsome man, whom the ladies desired, is really a woman. Anastasia gives her husband, Prosper, a box on the ear, and the baron exclaims 'Bravissimo! That is the reason for divorce!' Now the young couple will be free to marry. Cassim and Ninetta at last realise that they are cousins and quarrel unnecessarily about the same estate. As in almost every operetta, they all live happily ever after.

Berth Vestergaard