When Agrippina, wife of the Roman emperor Claudio, receives news of her husband’s death, she wastes no time in ensuring that Nerone, her son by a previous marriage, succeeds him. Prepared to go to any lengths to achieve her ends, she sends separately for Pallante and Narciso, of whose passion for her she is fully aware. She promises each of them in turn that she will reciprocate their love if they will proclaim Nerone as Claudio’s successor.
Her scheme is thwarted when Claudio’s servant Lesbo announces that the emperor’s life has been saved by Ottone, the commander of the army. When Ottone reaches the city, he declares that Claudio has rewarded his bravery by nominating him as his successor; but in a private conversation with Agrippina, he reveals that he loves Poppea more than the throne.
Agrippina now devises a fresh intrigue to secure the throne for Nerone. Aware that Claudio also desires Poppea, Agrippina tells Poppea that Ottone has betrayed her by yielding her to Claudio in exchange for the imperial throne. Agrippina suggests that, to avenge herself, Poppea must make Claudio jealous and convince him that Ottone, emboldened by his new status, has ordered Poppea to refuse Claudio and return to him: For this, the emperor will punish Ottone. When Claudio arrives, Poppea executes Agrippina’s plan.
Having discovered that Agrippina has deceived them, Pallante and Narciso decide to form an alliance. Ottone enters, apprehensive about the imminent public celebrations. The imperial family arrives, and when Ottone approaches the emperor, Claudio accuses him of treachery. To his increasing dismay, Ottone is shunned by Agrippina, Nerone, and Poppea.
Poppea begins to doubt Ottone’s guilt. Seeing him approach, she hides. When he sees her, she reveals to him what Agrippina told her. Ottone protests his innocence. Realizing that she has been a pawn in Agrippina’s plans, Poppea swears to be avenged and hatches a plot involving both Claudio and Nerone, who also desires her.
Ever ambitious, Agrippina has been plotting further to make Nerone emperor. First, she commands Pallante to murder Ottone and Narciso. Then, she asks Narciso to murder Ottone and Pallante. She tells Claudio that Ottone is seeking revenge on him for the loss of the succession and persuades him to suppress Ottone’s dissent by declaring Nerone as heir. Impatient to be with Poppea, Claudio agrees.
Poppea enacts her plan for revenge. She hides Ottone, telling him not to be jealous because of anything he overhears. Nerone arrives, eager to make love to Poppea, but she pretends that Agrippina is expected at any moment and he must therefore hide. Claudio enters, and Poppea complains that he does not truly love her. He reminds her of all that he has done for her, including Ottone’s punishment. At this, Poppea claims that he misunderstood her: It was Nerone, not Ottone, who constantly harassed her. Having hidden Claudio, Poppea calls to Nerone, who resumes his amorous pursuit of her; but Claudio interrupts and dismisses him. Poppea frees herself of Claudio on a pretext, and she and Ottone swear their eternal love.
Nerone recounts his disgrace to Agrippina and begs her to protect him from Claudio’s rage. Dismayed by all the treachery, Pallante and Narciso reveal Agrippina’s conspiracy to the emperor. When confronted by Claudio, Agrippina realizes that her schemes are now in jeopardy. She claims that she acted only in Rome’s best interests and accuses him of paying undue attention to Poppea. When Agrippina reveals that Ottone loves Poppea, Claudio lays the blame for his actions on Nerone, whom he commands to marry Poppea, and names Ottone as his successor. But Ottone renounces the throne in order to reclaim Poppea. Endorsing this exchange, Claudio nominates Nerone as his heir. Agrippina’s ambition for her son has finally come to fruition.