The action takes place in ancient Rome in the palace of the emperor Nero. He ascended the throne illegally, thanks to his mother Agrippina. Britannicus, son of Agrippina Claudius' second husband, was to become emperor, but she managed to bribe the army and the Senate and elevated her son to the throne. Nero, despite the influence of his highly moral mentors, the warrior Burr and the playwright Seneca, who is sent into exile, is already beginning to show his vile character and shows disrespect for his mother, to whom he owes everything. He does not hide his enmity towards Britannic, seeing him as an opponent.
Agrippina foresees that Nero will be a cruel tyrant, that he is lying and duplicitous. He abducts the beloved Britannica Junia, from the clan of the emperor Augustus, and keeps in his palace. Nero shuns her mother and does not listen to her advice on how to rule Rome. She would like to bring back the time when young Nero was not yet intoxicated by his power, did not know how to please Rome and transferred the entire burden of power to her mother. Then the “invisible” Agrippina, hidden behind the curtain, could hear everything that the senators invited to the palace told Caesar, and she knew how to govern the state, and told her son what to do. Now Agrippina accuses Burr of erecting barriers between her and Caesar in order to rule with him. Burr objects to her: he brought up the emperor, and not the humble servant, who will obey his mother in everything. Agrippina is hurt by the fact that her son rules independently, and believes that Nero impedes the marriage of Junia and Britannica, which she seeks, and thereby makes her mother understand that her opinion does not mean anything.
The Briton tells Agrippina that the legionnaires forcibly brought Junia to the palace at night. Agrippina is ready to help Britannic. He doubts her sincerity, but his mentor Narcissus assures him that Nero offended his mother and that she will act along with Britannic. The main thing, he advises, is to be firm and not complain about fate, for the power is honored in the palace and indifferent to complaints. The Briton in response complains that his father’s friends turned his back on him and Nero knows his every move.
In their chambers, Nero with Burr and Narcissus discuss the behavior of Agrippina. The emperor forgives much to his mother, who sets Britannica against him. Nero confesses to Narcissus that he is in love with Junia, and he reports that Caesar has a happy rival - Britannic. Nero wants to divorce his wife Octavia on the pretext that she does not have an heir to the throne. But he is afraid of a mother who will make a fuss if her son rises to the "sanctity of Hymen" and wants to break the bonds blessed by her. Narcissus promises to convey to Caesar everything he learns from Britannic.
Nero is going to upset the marriage of Junia and Britannica. Having met Junia in the palace, he admires her beauty. Junia says that marrying her with Britanic is the will of Father Britanic, the late Emperor Claudius, and Agrippina. Nero objects to her that Agrippina’s desire means nothing. He himself will choose the husband of Junia. She reminds Caesar that she cannot marry a person who is unequal in blood, because she is from the imperial family. Nero announces to her that he himself will be her husband, for in the whole empire he alone is worthy of such a treasure. Heaven rejected his alliance with Octavia, and Junia will rightfully take her place. Junia is astounded. Nero demands that Junia show coldness to Britannica, otherwise punishment awaits him. Nero will watch their meeting.
When meeting with Britannic, Junia begs him to be careful, because the walls have ears. The Briton does not understand why she is so shy, it seems to him that Junia forgot him and was captivated by Nero.
Having overheard their conversation, Nero is convinced that Britonik and Junia love each other. He decides to torture his opponent and orders Narcissus to kindle doubts and jealousy in Britannica. Narcissus is ready to do anything for the emperor.
Burr advises Nero not to quarrel with his mother, who has influence in Rome, and in order not to annoy Agrippina, he should stop dating Yunia and leave thoughts of a divorce from Octavia. Nero does not want to listen to his mentor and declares that it is not the warrior’s job to judge love - let Burr advise him on what to do in battle. Left alone, Burr reflects on how willful Nero does not listen to any advice, wants everything to be done according to his will. Is it dangerous. Burr decides to consult with Agrippina.
Agrippina accuses Burr that he could not keep in check the young emperor, who had removed his mother from the throne, and now also wants to divorce Octavia. Agrippina is plotting with the help of troops and Britannic to regain his power. Burr does not advise her to do so, for no one will listen to Agrippin, and Nero will only become enraged. The emperor can only be persuaded by "meekness of speech."
The Briton tells Agrippina that he has accomplices in the Senate, ready to oppose the emperor. But Agrippina does not want the help of the Senate and is going to threaten to force Nero to abandon Junia, and if this does not help, then notify Rome of Caesar's plans.
The Briton accuses Junia of having forgotten him for the sake of Nero. Junia begs to believe her and wait for "better days", she warns Britannic that he is in danger, for Nero overheard their conversation and demanded that Junia reject Britannic, threatening him with reprisal. Nero appears and demands that Britannic obey him. He indignantly replies that Caesar has no right to mockery, violence and divorce from his wife, that the Roman people will not approve of the emperor's actions. Nero believes that the people are silent, and this is important. Junia begs Nero to spare Britanic, because this is his brother (Britonic's father adopted Nero), and for the sake of reconciliation she is ready to become a vestal. The emperor becomes furious and orders to take Britannic into custody. He blames Agrippina for everything and orders the guard to be assigned to her.
Agrippina and Nero meet, and Agrippina pronounces her famous monologue about how many atrocities she committed in order for Nero to become emperor. She bribed the Senate, which authorized her marriage to her uncle, Emperor Claudius. Then she begged Claudius to adopt Nero, then, by her slander, Claudius alienated all those who could help his son Britannic inherit the throne. When Claudius died, she hid it from Rome, and Burr persuaded the troops to swear allegiance to Nero, and not to Britannica. Then the double message was immediately announced to the people: Claudius was dead, and Nero became Caesar. Instead of gratitude, the son moved away from his mother and surrounded himself with dissolute youths.
Nero in response tells his mother that she did not bring him to the throne in order to rule him and the power. After all, Rome needs a lord, not a mistress, Nero accuses his mother of conspiring against him. Agrippina replies that he has lost his mind, that she devoted her whole life only to him. She is ready to die, but warns Caesar that the Roman people will not forgive this to Nero. Agrippina demands that Nero let go of Britannic and not quarrel with him. He verbally promises to fulfill everything.
When meeting with Burr, Nero tells him that it is time to put an end to Britannic, and then his mother will be easily tamed. Burr is terrified, and Nero says that he is not going to reckon with the opinion of the people and he does not care about blood. The burr calls on Caesar not to embark on the path of evil, for it is a bloody path - the friends of Britannic will raise their heads and begin to take revenge, a terrible enmity will flare up, and an enemy will appear in every subject Caesar. It is much more noble to do good. Burr on his knees begs Nero to make peace with Britannic. He is inferior. Narcissus comes to Nero and says that he took from the well-known in Rome poisoner Lokusta a quick poison to poison Britanic. Nero hesitates, but Narcissus scares him because Britannicus can learn about the poison and begin to take revenge. Nero replies that he does not want to be considered a fratricide. Narcissus, on the other hand, calls on Caesar to be higher than good and evil and not to depend on anyone - to do only what he considers necessary. Kindness only testifies to the weakness of the ruler, but all bow to evil. If Nero poisons his brother and divorces his wife, no one in Rome will say a word to him. Nero must shut up his mentors Burr and Seneca and rule himself.
Meanwhile, Britannic informs Junia that Nero has reconciled with him and is convening a feast in honor of this. The Briton is glad that now there are no barriers between him and Unia. But Junia is alarmed, she foresees misfortune. Nero cannot be trusted, he is a terrible hypocrite, as is his entourage. She believes that this feast is just a trap.
Agrippina appears and says that Britannica is waiting for everyone, and Caesar wants to raise the cup for their friendship. Agrippina assures Junia that she has obtained from Nero everything she wanted, that he no longer has secrets from his mother, and that he is not capable of doing evil things.
Burr runs in and reports that Britannic was dying, that Nero skillfully hid his plan from everyone and at the feast gave Britannic a cup of wine in which Narcissus put poison. The Briton drank for friendship with Nero and fell lifeless. The environment of Nero calmly looked at the emperor, but his eyes were not clouded. Narcissus could not hide his joy. Burr left the room.
Agrippina tells Nero that he knows who poisoned Britanic. He with ostentatious surprise asks who she is talking about. Agrippina answers - it was he, Nero, who committed the murder. Appeared Narcissus betrays Caesar and declares that there is no need to hide his affairs. Agrippina bitterly reproaches Nero for having chosen Caesar as worthy accomplices and as equally worthy of starting with the poisoning of his brother. Now the turn, apparently, is behind her. But the death of his mother will not be in vain - conscience will not give rest, new murders will go and in the end Nero will fall a victim of his own atrocities.
Left together, Agrippina and Burr say that death awaits them and they are ready for it - Caesar is capable of anything. A friend of Agrippina Albina appears and reports that, having learned of the death of Britannicus, Junia rushed to the square to the statue of Augustus and, among the people, begged him to let her become a vestal and not be disgraced by Nero. The people led her to the temple. Nero did not dare to intervene, but the obedient Narcissus tried to prevent Junia and was killed by the crowd. Seeing this, Nero, in impotent rage, returned to the palace and wanders there. He's up to something. Agrippina and Burr decide once again to appeal to the emperor’s conscience and prudence in order to prevent evil.
