The place and time of events the author precisely indicates at the end of the list of characters – Genoa, 1547. The play is preceded by the epigraph of the Roman historian Sallustius about Catalina: “I consider this villainy out of the ordinary by the unusualness and danger of crime.” The young wife of Count Fiesco di Lavagna, the leader of the Republicans in Genoa, – Leonora is jealous of her husband to Julia, the sister of the ruler of Genoa. The count really takes care of this flirtatious widow, and she asks Fiesco for a love of love to give her a medallion with a portrait of Leonora, he also gives his own.
The nephew of Doria, the ruler of Genoa, Gianettino suspects that in Genoa Republicans are plotting against his uncle. To avoid a coup, he hires the Moor to kill the head of Republicans Fiesco. But the treacherous Moor gives the plan to Gianettino to Count di Lavagna and goes to his service.
In the house of Republican Verrina is a great grief, his only daughter Bert was raped. The criminal was wearing a mask, but according to the description of his daughter, the unfortunate father guessed that it was the work of Doria’s nephew. Coming to Verryna to ask for Bertha Borgonino’s hands, she witnesses the terrible curse of her father; he locked his daughter in the dungeon of his own house, until the blood of Gianettino would wash away the disgrace of his kind.
Fiesco comes to the nobles of Genoa, they tell him about the
To Gianettino is his trusted Lomellino. He warns the nephew of Doria of the danger looming over him in connection with the betrayal of the Moor. But Gianettino is calm, he has long stocked the letter with the signature of Emperor Charles and his seal. It says that the twelve senators of Genoa must be executed, and the young Doria will become a monarch.
In the house of Fiesco come Genoese patrician Republicans. Their goal is to persuade the count to take charge of the conspiracy against the duke. But di Lavagna outstripped their proposal, he shows them letters, in which the soldiers from Parma, “gold from France”, “four galleys of the Pope of Rome” are reported to arrive in Genoa for “deliverance from tyranny”. The nobles did not expect such a quickness from Fiesko, they agree on a signal for the performance and diverge.
Along the way, Verrin entrusts his future son-in-law Burgonino with the secret that he will kill Fiesco as soon as Dorian’s tyrant is overthrown, for the visionary old Republican suspects that the goal of the count is not the establishment of a republic in Genoa. Di Lavagna himself wants to take the place of the duke.
Maurus, sent Fiesko to the city in order to find out the mood of the Genoese, returns with a message about the intention of Gianettino to execute twelve senators, including the count. He also brought a powder, which the Countess of Imperial asked him to pour into a cup of chocolate Leonore. Fiesko urgently convenes the conspirators and informs them of the emperor’s letter to Doria’s nephew. The uprising must begin that night.
In the late evening in the house of Fiesco, the Genoese noblemen gather, supposedly to represent the comedians. The Count pronounces a fiery speech, in which he calls them to overthrow the tyrants of Genoa, and hands out arms. The last to break into the house is Calcano, who is just from the palace of the duke. There he saw the Moor, he betrayed them. All in confusion. In an effort to master the situation, Fiesco says that he himself sent his servant there. There are German soldiers guarding the Duke Doria. They enter the Moor, with him a note in which the tyrant of Genoa informs the count that he is notified of the conspiracy and will purposely send his bodyguards tonight. Nobility and honor do not allow Fiesko in such a situation to attack Doria. Republicans are adamant, they demand to lead them to storm the ducal palace.
Julia is also invited to represent the imaginary comedians in the house of the Count. In front of his wife, Leonora Fiesco plays the stage, seeking recognition from the Countess of Imperial in love. Contrary to expectations, Count di Lavagna rejects the ardent love of an insidious flirt, he calls the nobles in the house, returns Julia when witnessing the powder she wanted to poison his wife, and the “foolish trinket” – a medallion with her portrait, and the countess herself orders to be arrested. Leonora’s honor is restored.
Left alone with his wife, Fiesko admits to her in love and promises that soon she will become a duchess. Leonora fears power, she loves a solitary life in love and harmony, to this ideal, she tries to persuade her husband. Count di Lavagna, however, is no longer able to change the course of events, a cannon shot sounds – a signal for the beginning of the uprising.
Fiesco rushes to the duke’s palace, changing his voice, he advises Andrea Doria to flee, the horse waits for him at the palace. He at first does not agree. But, hearing the noise in the street, Andrea runs under the cover of the guards from the palace. Meanwhile, Bourgoigno kills Doria’s nephew and hurries to Verrina’s house to inform Berthe that she is avenged and can leave her prison. Berta agrees to become the wife of her protector. They flee to the harbor and leave the city on the ship.
Genoa is in a state of chaos. Fiesco meets a man on the street wearing a purple cloak, he thinks it’s Gianettino, and stabs the duke’s nephew. Rejecting the cloak of the murdered, di Lavagna learns that he killed his wife. Leonora could not stay at home, she rushed into the battle to be next to her husband. Fiesco is heartbroken.
The Duke of Andrea Doria can not leave Genoa. He returns to the city, preferring death to eternal wandering.
After recovering from Leonora’s death, Fiesco dressed in a purple cloak, a symbol of the ducal authority in Genoa. In this form, Verrin finds him. The Republican proposes the count to throw off the clothes of the tyrant, but he does not agree, then Verrin carries Di Lavagna to the harbor, where, when climbing the gangplank, Fiesko is thrown into the sea. Confused in a raincoat, the Count sinks. Hurrying to the aid of the conspirators tell Verryne that Andrea Doria returned to the palace and half Genoa passed to his side. Verrin also returns to the city to support the ruling duke.