The play has yet to begin but already the personages, who in all the scenes which follow will appear in the role of stage audience commentating on and caught up in the performance, are engaged in fierce argument about it. The Tragedians demand tragedy, grief and assassinations; the Comedians - comedy and invigorating laughter; the Romantics - lyrical drama, romantic love, flowers, tender kisses; and the Empty Heads - farces and amusing frivolities. Slanging matches which all but develop into fights, are underway. Only the Eccentrics are in peaceful mood: they part the contestants and invite them to watch the performance.
The Herald announces: "The King of Clubs is in despair: the Prince, his son and heir apparent, is suffering from hypochondria!"
The royal palace. The King and his adviser, Pantalone, are listening to the doctors' verdict on the Prince's deplorable state of health. The King is really worried: he is getting old, what will happen to his kingdom? Who is to succeed him? Surely not his niece, the odious Clarice? Suddenly the King remembers that the doctors once told him the only way of saving the Prince was to make him laugh. Pantalone pricks up his ears: they must announce a festivity, with games and masquerades…He immediately summons Truffaldino: for if anyone can make a man laugh he can.
Prime Minister Leandro who wishes the Prince ill and wants him to die tries, under various pretexts, to dissuade the King. But the King insists his order be carried out.
The scene moves to the world of the cabala. The Magician Celio appears from flames and smoke. Immediately, and with an equally loud thunderclap, Fata Morgana steps out of the smoke too. The Little Devils run up. They prepare the cards. The game starts. Celio keeps losing. Fata Morgana is triumphant. The Eccentrics are anxious for the King and the Prince: for it is their fates that are now being played for by the two magicians.
The royal palace. Leandro is concocting his devious plans. "Remember, if the Prince dies, and I become heiress to the throne, I will marry you!", says Princess Clarice, urging him on. Leandro assures her that his method is slow but true: he is filling the Prince full of tragedies and utterly boring verse. Truffaldino appears. Leandro and Clarice are taken aback: this man knows how to make people laugh, he may undermine their plans. Clarice demands action from Leandro: "The Prince must be given opium or a bullet".
Suddenly Leandro discovers that Smeraldina, the negress, is eavesdropping. He threatens to kill her. But it turns out that Smeraldina is not an enemy, but the accomplice of Fata Morgana. She reveals to Leandro that Truffaldino is going to help the Prince and that the Magician Celio is favorably disposed to the latter. Smeraldina promises to help Fata Morgana. The Prince will never laugh with her about.
The Prince's room. The prince in deep gloom is watching the comic dance organized by Truffaldino. But all attempts to make the Prince laugh are in vain.
Truffaldino throws away all the Prince's medicines. This makes the Prince angry and he runs off. The assembled company hurries after him.
At the royal palace the performance is about to begin. It is directed by the ubiquitous and irrepressible Truffaldino. The "Monsters" amuse the audience. All are in paroxysms of laughter except for the Prince who remarks glumly: "The noise is deafening me".
Disguised as an old hag, Fata Morgana manages to enter the palace. "The Prince won't laugh with me here", she whispers to Leandro.
A new diversion starts. Truffaldino orders the fountains to be turned on. Butter spurts from one, and wine from another. A crowd of "drunkards" and "gluttons" are turned loose. Amidst the general merriment, the Prince remains glum and asks to be carried back to his warm bed. Truffaldino is close to despair: he is running out of ideas. Catching sight of Fata Morgana, he tries to chase her away. Fata Morgana refuses to be ejected and Truffaldino impatiently gives her a shove: "Be off with you, you cursed hag!" Fata Morgana loses her balance. As she falls, she gives a shriek: her absurd pantaloons come into view. And suddenly the Prince starts to laugh: "What…a funny… old woman!" In their delight, all those present start dancing, even the old King jumps up and down on his throne. The only people who do not take part in the general merriment are Clarice and Leandro.
Roused to fury, Fata Morgana curses the Prince: it will be his fate to fall in love with three oranges, and he will pursue them to the ends of the earth.
The Prince is transformed. He is now full of energy. Despite the King's command that he remain in the palace, the Prince, taking Truffaldino with him, sets off in search of the three oranges, in search of happiness and love.
The desert. The Magician Celio summons Farfarello, the Devil, from the darkness. The latter informs Celio that the Prince and Truffaldino are in hell, at the castle of Sorceress Creonte. Celio tries in vain to restrain Farfarello but the latter, saying that there is nothing doing since Celio lost his friends at cards, disappears with a chuckle.
The Prince and Truffaldino appear. They know the oranges are at Creonte's castle, where they are guarded by the terrifying and all-powerful Cook. But the Prince is afraid of nothing. He is in love, he must find the three oranges! Realizing he does not have the power to stop the Prince, Magician Celio presents him with a magic ribbon in the hope it may distract the Cook's attention. He also gives him an important piece of advice: the three oranges may be cut open only near water, otherwise disaster will strike.
With a puff of wind, Farfarello literally wafts the Prince and Truffaldino into Creonte's castle. Here these unwanted guests will perish! Remembering the advice of Magician Celio, the Prince and Truffaldino make their way stealthily to the kitchen. A terrifying rumbling is heard. The Cook appears with a huge spoon. She suddenly catches sight of Truffaldino and begins to shake him furiously when she notices the beautiful ribbon. The Cook falls hopelessly for the ribbon and this appeases her wrath. Making a sign to the Prince, Truffaldino starts to flirt with the Cook and presents her with the ribbon. Truffaldino seizes the oranges (the size of a human head) and, together with the Prince, makes his getaway.
The Prince and Truffaldino are wandering over the desert: they are pulling the three oranges behind them on a string. During the long journey, the oranges have grown to huge dimensions, big enough, one might think, to contain a human being. The Prince who is very tired, falls to the ground and nods off. Truffaldino is tormented by thirst, and he decides to cut open one of the oranges to drink from it. Out of the orange steps a maiden dressed in white - Princess Linetta. She begs for water, otherwise, she says, she will die of thirst. But all round them is desert. In order to save the Princess, a scared Truffaldino opens the second orange. And, would you believe it? Out of it steps Princess Nicoletta who also implores to be given water, even if only a drop. A horrified Truffaldino watches while both princesses die. Aghast at what he has done, he rushes off.
On waking up, the Prince sees the only remaining orange. He splits it open with his sword and before him appears a beautiful maiden in white, Princess Ninetta. The Prince falls to his knees before her: "Princess, I have been looking for you all over the world. I love you more than the whole world put together!" But Ninetta is growing weaker by the minute, she begs for a drop of water. At this point - O heavens be praised - the Eccentrics appear on the scene and save the situation. They are pulling a rain cloud behind them. The Princess is saved! At long last, she is united with her loved one. She asks the Prince to inform his father, the King, of what has happened and to bring her some suitable, royal clothing. The Prince leaves to do her bidding.
Smeraldina and Fata Morgana now appear. Running up behind Ninetta, Smeraldina sticks a long, magical pin into her head. Ninetta is kidnapped by a huge rat. Fata Morgana orders Smeraldina to take Ninetta's place and tell everyone that she is the Princess.
A solemn procession appears with the King and Prince at its head. They are followed by Clarice, Leandro, Pantalone, courtiers and guards. The Prince runs up to a female figure standing alone and exclaims joyfully: here is my Princess! But he immediately steps back in dismay: it is not her! Smeraldina reminds the Prince that he promised to marry her. The Prince is horrified, but the King insists he keep his word. Leandro comments maliciously: "The orange has begun to rot!"
In the world of the cabala, Magician Celio and Fata Morgana are at each other's throats again, cursing and abusing each other. The Eccentrics manage to lure Fata Morgana into a trap and close the door firmly on her! Smoke pours out of the trap. Now Celio will be able to help his friends without hindrance.
In the royal throne-room, the King is expected any moment. A procession starts. The Master of Ceremonies orders that the velvet covers be taken off the thrones of the Prince and Princess. Suddenly a huge rat appears. Everyone is taken aback. Eventually, Magician Celio manages to lift Fata Morgana's curse. The King shoots the rat. And in its place stands the beautiful Princess Ninetta. The evil powers are dispersed.
The Prince throws himself on his knees before Princess Ninetta: "My love! My little orange!" On learning the truth, the King decides to punish the evil conspirators - Clarice, Leandro and Smeraldina. Anxious lest a shadow be cast over the happy ending. Truffaldino pleads with the King to show leniency to the conspirators. But the King is adamant: he demands a rope - all the culprits shall be hanged. The guilty trio attempt to escape. Determined the traitors shall not get away, everyone sets off in pursuit. Suddenly, Fata Morgana appears and summons the fugitives to her side. They jump into the trap and from it - flames and smoke emerge! The guards running, but they are too late: they find nothing but an empty, flat stretch of ground.
A happy finale. The assembled company joyfully drink a toast to the King, the Prince and the Princess.