In the tent of Demetrius, the Grand Duke of Moscow, there is a military council. The prince calls to fight with the Tatars: now that the Kirchak Horde has broken up and the khans are fighting for power, the combined Russian troops will be able to defeat Mamaia, who goes to war with them. Dimitri is convinced that Mamai doubted the success of his campaign as soon as he learned that the combined forces of the Russians crossed Don. Demetrius invites the princes to decide whether to accept the embassy that Mamai sent to them or not. Prince of Tver against negotiations with the Tatars. Reminding those present that his bride should soon arrive in the camp, Princess Ksenia of Novgorod, Prince Tverskoy declares that he will lead her to the crown only after the battle and will present her father’s armor with the gift. Prince Belozersky proposes to receive ambassadors. He believes that it is necessary to make peace and pay tribute to Mamaia: in this way Christian lives will be saved. In addition, Prince Belozersky fears that the victory over the Tatars will force the enemies to unite and all the khans will attack Russia together. Demetrius, after hearing the opinions of his allies, agrees to receive the ambassador from Mamai, but declares that he prefers death in battle to a humiliating world.
The ambassador is trying to intimidate the Russian princes. He says that they are "nine hordes and seventy princes", but Mamai is ready to keep his troops, forgive the Russian princes who dared to oppose him, and agrees to pay tribute to them. When Demetrius refuses, the ambassador, turning to all the princes, declares that the one who comes to Mamaia with the head of Demetrius will own the throne and Moscow. Outraged by this insolence, the princes are ready to fight with the Tatars.
The Tver prince proposes to cross the Nepryadva River and be the first to attack the camp of Mamaia. Dimitry appoints him to command the right wing of the troops, Prince Smolensky - the left, brother Dimitri with a large regiment will be ambushed behind the forest, and Dimitri himself will lead the main regiment.
When Dimitri and his squire, Mikhail Brensky, are left alone, Michael exhorts the prince so that he overcomes the pernicious passion for Princess Novgorod Ksenia, who, by the decision of her father, should become the wife of Prince Tversky. Demetrius tells Brensky how he confessed Xenia to love in the presence of her mother, and hoped that the marriage with Prince of Tver would not be completed, because the girl reciprocated with him, Demetrius. However, the princess died, and when Demetrius was going to ask Xenia’s hands for her father, Mamai went to Russia with war. Brensky is ashamed of Demetrius: the alliance of the Prince of Tver with Xenia has already been decided and her father is going to send her daughter to the camp. At this time, Demetrius was informed of the arrival of Princess Xenia.
Ksenia confesses to her confidante Elect that she will not become the wife of the Prince of Tver and will bring a monastic vow. The chosen one persuades the princess to confess to her father that she loves Prince Demetrius, but Ksenia does not dare to go against the will of her parent. Dimitri comes, blinded by rage, threatens to go to war on her father. The prince of Tver appears. Ksenia tells him that her parent was not thinking about the daughter’s happiness, but about saving the fatherland, when he announced to all the princes his decision to unite his family with the Tverskoy family: so her father hoped to induce the Russian princes to fight the Tatars. The princess informs Prince Tversky that she is going to become a nun, and leaves for her tent. Dimitri in the presence of Prince of Tver hides his feelings, but when he tells him that after winning Mamai, he will force Ksenia to marry him right in the camp, Dimitri stands up for the girl and admits that he loves her. The prince of Tverskaya reproaches Demetrius for autocracy, threatens to withdraw his regiments that night and is going to tell about all the rest of the princes.
The princes are outraged that Demetrius does not respect the rights of Prince of Tver. Prince Smolensky is sure that the autocracy of Demetrius threatens them all: if the greedy Horde wants only gold, then the autocratic despot “puts a heavy chain on all deeds,” enslaving both thought and feeling. Prince Smolensky prefers to make peace with the Tatars, than to see an equal race by his lord over himself and other princes.
Dimitri comes and tells that at night Mamai moved on them. He calls on the princes to come together against the enemy. Prince Belozersky demands from Demetrius that he prove to them his love for the fatherland and be reconciled with the Prince of Tver: let his marriage to Xenia be the key to reconciliation. Demetrius replies that honor tells him to protect the girl, who against her will must go down the aisle. Demetrius condemns the customs that “make tyrants out of their fathers and introduce their children to the murmuring of slaves.” Belozersky objects, pointing out that only there is morality in the people where the rights of the fathers are sacred. Demetrius stands his ground. Princes accuse him of pride and refuse to participate in the battle. Demetrius declares that he will fight with Mamai alone. When everyone leaves, Demetrius sends Brensky to Xenia, so that he persuades her to come to him and tells how desperate he is and how he needs comfort.
The night is coming. Demetrius goes to the tent to the Moscow boyars. He asks them if they still want him to fight Mamai. Those support the decision of the prince, swear allegiance to him and are ready to go to death with him.
In front of his tent, Demetrius meets Ksenia with Chosen and Brensky. Demetrius tells the princess that the hope of her love will give him strength in battle. Let all the princes leave him: "the prince is safe among zealous citizens, where there are a host of boyars of wisdom, where a host of nobles is faithful." Ksenia is in despair: she is afraid that the army of Demetrius will be defeated, and Russia will languish under the Tatar yoke. She calls on the princes and blames herself for all the discord between Demetrius and the Prince of Tver. She asks the Prince of Tver to punish her for violating her father’s word. Ksenia is ready to go to the most remote monastery, but let the princes reunite and fight with the hordes of Mamaia. When the prince of Tver nevertheless refuses to join Demetrius, Ksenia agrees to become his wife. The princes approve of her decision and agree to fight with Mamai.
Demetrius and Prince of Tver are ready to go on a duel with each other, but Ksenia does not allow this. Then the prince of Tver tells Demetrius that they should reveal on the battlefield which of them is more worthy of Princess Xenia. When everyone leaves and Dimitry stays with Brensky, he asks the faithful squire for the last service: let Michael stand in his place under the banner and put on his helmet and signs of princely dignity. The prince himself will dress like a simple warrior, for he will now seek dangers and death. Demetrius gives Brensky a chain from his chest so that he passes it to Xenia when he is no longer alive.
Ksenia and Chosen are hiding in a valley between the mountains. They witnessed the flight of Russian troops and are sure that Demetrius was dead. They meet the Moscow boyar with several warriors and talks about the victory over Mamai. At the beginning of the battle, the Tatar knights Temir and Chelubey scattered the ranks of Russian soldiers. Then the monk Peresvet called Temir to a duel, and both fell dead, and an unknown warrior in simple clothes attacked Chelubey and killed him. After this, brother Dimitri hit the Tatars from the rear from the nearby forest, and they shamefully fled. Among the dead and wounded Russian warriors, everyone is looking for Demetrius and the unknown warrior, the winner of Chelubey, but they only find the dead Brensky in princely armor. Finally they discover an unknown warrior covered in wounds, and they recognize him as Demetrius. The prince hopes for death, for life was not sweet to him without his beloved. The Prince of Tver, shocked by these words, generously gives Xenia to Demetrius. Everyone celebrates the victory of Russian weapons and congratulate Prince Demetrius on the victory.
