In the anteroom of the imperial palace Agrippine waits to speak with Néron, her son. The impatient nature of his character at last reveals itself in antagonistic behavior toward Britannicus, and Agrippine fears that she will next incur his disfavor. Albina is convinced of the emperor’s continued loyalty to his mother. Agrippine feels that if Néron is indeed noble, the fact that she wins the throne for him will ensure his devotion; but if he is ignoble, the fact of his obligation will turn him against her.

On the previous night Néron abducted Junie, to whom Britannicus is betrothed, a deed possibly motivated by resentment against Agrippine, who begins to support Britannicus in an attempt to preserve her position in the future if Néron is to turn against her. Albina assures Agrippine that her public power and honor, at least, are not decreasing. Agrippine, however, needs the assurance of a more personal trust. She confides that once Néron turned her aside from the throne on which she customarily sits in the Senate. She is also denied all private audiences with him.

Agrippine, reproaching Burrhus for disloyalty to her, accuses him of attempting to gain power over Néron. Burrhus is convinced that his prime loyalty is to the emperor, who rules well by his own authority. Néron fears that Britannicus’s children will inherit the throne if he marries Junie. Britannicus, distracted by his loss of Junie, complains of Néron’s harshness. Agrippine sends him to the house of Pallas, the freedman, where she will meet him later. Britannicus tells Narcisse, who encourages him to join Agrippine, that he still wishes to claim the throne.

Néron decides to disregard his mother’s reproaches, which he calls unjust, and to banish Pallas, the friend and adviser of Agrippine, who, he thinks, corrupts Britannicus. Narcisse assures him that Rome approves of his abduction of Junie, and Néron confesses that when he saw her he fell in love with her. He is convinced by Narcisse that Britannicus is devoted to Junie and that she probably loves him in return. Narcisse insists that the love of Junie will be won by a sign of favor from the emperor. Narcisse advises Néron to divorce Octavia, Britannicus’s sister, and marry Junie. Néron fears Agrippine’s wrath if he does so; only when he avoids her completely does he dare defy her wishes, for in her presence he is powerless. Narcisse informs Néron that Britannicus still trusts him; he is therefore dispatched to bring Britannicus for a meeting with Junie. Junie asks Néron what her crime is and insists that Britannicus is the most suitable person for her to marry, as he is the only other descendant of Augustus Caesar at court. When Néron says that he himself will marry her, Junie, appalled, begs him not to disgrace Octavia by doing so. Finally she realizes that she can save Britannicus’s life only by telling him, when they meet, that he is to leave Rome. Néron intends to listen to their conversation.

At their interview, Britannicus is bewildered by Junie’s coldness toward him and by her praise of the emperor. When he leaves, Néron reappears, but Junie flees, weeping. Néron sends Narcisse to comfort Britannicus. Burrhus reports that Agrippine is angry at Néron, and he fears that she might plot against the emperor. When Néron refuses to listen to Burrhus as he begs him not to divorce Octavia, the tutor realizes that the emperor’s true character is at last appearing.

Meanwhile, Agrippine plans to take Britannicus before the Roman army and to declare that she wronged him by exalting Néron to the throne....