The action takes place in an old castle in Spain, the home of Corradino, known as Cuor di Ferro (Iron-heart) for his complete dedication to the martial arts and for his reputation as a fierce and unpredictable man.His ferocious nature would seem to be confirmed by two threatening signs hanging amongst the trophies of battle that decorate his castle courtyard. One of these reads "Whoever enters here uninvited will be rewarded with a broken skull", and the other "Whoever dares to disturb my peace will die here of hunger and thirst". Amongst Corradino’s servants are Ginardo, the tower-keeper, and Aliprando, the physician. A group of peasants, led by Egoldo, reach the castle. They have brought gifts of fruit and vegetables for their lord, but they soon decide to run away, equally frightened by the two signs and by the warnings of Aliprando, who in menacing tones describes the cruelty of Corradino towards men and his hatred of the female sex. The next to arrive at the castle is a certain Isidoro, a would-be poet who has ended up in Spain, having set off from Naples with nothing other than his guitar, hoping to find somewhere a patron disposed to maintain him in exchange for his literary services. His meeting with Corradino, however, is not promising; the misanthropist, in fact, decides to kill him merely for the offence of having crossed the threshold of the castle. Aliprando tries to intercede for the unhappy poet, but to little or no effect: Corradino, convinced that the intruder is either an assassin or a spy, orders his soldiers to lock him up in prison. Aliprando now tries to distract him from his murderous intentions by telling him that Matilde di Shabran, daughter of a valiant soldier who, before dying on the field of battle, made Corradino promise to look after her, proposes to pay him a visit. The ferocious lord of the castle agrees to receive her only out of respect for her late father’s courage. Meanwhile he orders Edoardo, a young nobleman, son of Raimondo Lopez, to be brought before him once more: Corradino is keeping him prisoner in the castle merely because, after having been beaten in battle by Corradino, he proudly refuses to acknowledge himself beaten and to kneel at the victor’s feet.
When the two have finished their parley, to no result whatever, Matilde enters, accompanied by Aliprando. The young lady intends to make Iron-heart fall in love with her, even though Corradino has scorned women all his life. Matilde’s little plan immediately finds an obstacle in the shape of a rival, the Contessa D’Arco, who is also staying at the castle and who has no intention of allowing Matilde to win the prize. Some time ago, in fact, Corradino had become engaged to be married to the Contessa as part of the articles of a peace-treaty. Afterwards he has always managed to put off the dreaded hour of matrimony by promising her family that at least he would never marry any other woman. The two rivals for the warrior’s apparently impregnable heart have it out in a violent row, after which Matilde even manages to calmly ignore some rude comments of Corradino, who is struck dumb by her behaviour. When Matilde openly provokes the Contessa, the outraged noblewoman is overcome with anger because of the insult. Corradino, however, does not seem capable of reacting in any way: confused and uncertain, he asks himself whether he should have the newly-arrived guest locked up in chains or send her away, whilst his blood courses tumultuously through his veins. Iron-heart is new to the pangs of lovesickness, which are even now fatally undermining him: he feels as though he is all on fire, and orders his physician to diagnose at once the cause of this unfamiliar fever and cure him of it without delay. When Aliprando proves quite unable to give him any relief, Corradino begins to suspect that he is under a spell, perhaps put on him by Isidoro. He orders the unfortunate poet to be brought before him, he questions him and declares without compunction that he is a magician, and condemns him to death. But now the fair Matilde appears; Corradino no longer knows whether he should avoid her, as the cause of his mysterious illness, or seek her company for the sake of the painfully mysterious pleasure that he takes in it. Her every word pierces him like an arrow, and, deeply moved, he kneels before her and declares his love, oblivious of the onlookers who laugh at him behind his back. Love has transformed the indomitable lion into a quivering little lamb.
Suddenly an alarm bell and a roll on the drums announce the sighting of a number of armed men led by Edoardo’s father, who is advancing towards the castle in search of his son. Rodrigo, leader of the castle troops, prepares to lead his men out to the fray. Matilde, Ginardo, Aliprando and the Contessa all prepare to leave the castle together with Corradino and his men. The banner of the picturesque army is held aloft by Isidoro, who now considers himself fully established as court poet, and so prepares to celebrate in verse the achievements of his warlike lord. Hearing what is happening, Edoardo bursts into tears, fearing that his father’s life is in danger. Matilde intercedes on his behalf, begging Corradino to act with humanity and mercy at the last. This action of hers, however, arouses in him the dread suspicion that she is prompted by tender feelings towards the young prisoner. Although there are no grounds for this suspicion, Corradino begins to feel himself devoured by jealousy, seeing which the Countess becomes herself livid with jealous fury; here is the final proof, after all, that her rival has triumphed over his heart.
In a secluded part of the countryside around the castle, Isidoro, who has managed to remove himself from the heat of battle, is preparing to write down his military memoirs, puffing himself as the hero of wildly improbable feats of valour: however, according to him, it is the Muse of Poetry herself who inspires his inventive tale. Raimondo appears; his men have fled during the battle and he has lost all hope of ever seeing his son again. Edoardo, for his part, once more enjoying his freedom, which he believes he owes to Matilde’s intervention on his behalf, calls upon death to release him from his sufferings, for he believes that his father has been killed in the battle. He is therefore almost overcome with joy and relief when, in the distance, he hears his father’s voice calling his name. Corradino now comes on and is furious when he finds Edoardo enjoying his freedom. When Edoardo tells him that it was the fair Matilde herself who caused him to be freed from his chains, Corradino, believing that she has betrayed him, vents all his rage upon her. Meanwhile, at the castle, where Matilde is anxiously awaiting the outcome of the battle, the Contessa is plotting her downfall: it was she, in fact, who bribed the jailer to set Edoardo free, and to expose the innocent Matilde, her rival, to the full force of Corradino’s anger.
When Isidoro returns the two women eargely ask him for news: naturally enough, the poet gives himself credit for some extraordinary feats of military valour, claiming, in fact, to have been solely responsible for the victory. Ginardo and Aliprando have to bring him down to earth by telling the truth: Raimondo’s troops immediately gave way before the onslaught of Corradino’s; Corradino has gone into the forest alone in order to challenge Raimondo to single combat. Matilde is trying to persuade them to go out and search for him, when a drum-roll announces his return. As soon as he enters the castle, Corradino accuses Matilde of having set Edoardo free. The young woman’s position is complicated by the arrival of the captain of the castle troops with a mysterious letter addressed to her: the Contessa makes him hand it over to her, and she reads it out: it is from Edoardo, who passionately thanks the lady to whom he believes he owes his freedom. All the Contessa has to do now is openly accuse Matilde of treason, and Matilde tries in vain to defend herself. Where everybody else is full of astonishment and doubt, Corradino himself is absolutely sure: he orders Isidoro to throw the young lady into a rushing river at the bottom of a gorge near Raimondo’s castle. He then retires to brood over his own mistakes: the mere fact that she was a woman should have been enough to warn him not to trust Matilde from the start... Isidoro comes back and entertains the fierce lord of the castle with a detailed poetic description of the executing of his orders; the Contessa, at long last, feels all the satisfaction of revenge. But Edoardo now comes in and reveals to Corradino that it was not Matilde who set him free, but the jailer Udolfo, who had been bribed by the Contessa, who hoped in this way to get rid of her rival. Iron-heart is thrown into the deepest despair by this news.
Crushed by remorse, he decides to join his beloved in death, and goes out into the night to throw himself into the same abyss. Ginardo and Aliprando are trying to dissuade him when Edoardo comes out of his castle, leading Matilde by the hand, alive and well: it was true up to a point that Isidoro had «killed» her, but only «metaphorically; in a manner of speaking, by poetic licence». Corradino throws himself at the feet of his beloved and begs her to forgive him. In exchange for her forgiveness, Matilde demands that he should open his heart to kindness and be reconciled with Raimondo. As far as the Contessa is concerned, seeing Matilde alive will be punishment enough for her. Now it is time for Isidoro to compose a nuptial sonnet, and the curtain falls on Matilde’s song of praise to love and to the triumph of femininity.
Synopsis courtesy of the Rossini Opera Festival, Pesaro, Italy