The action takes place at the end of the 6th - beginning of the 7th centuries, at a time when Kiy ruled in Russia, and his power was strong and undeniable.
Sixteen years ago, Kiy ousted from the throne Zavlokh, Prince of Kiev, to reign in his place. In that battle, the sons of Zavlokh were killed, and the defeated prince himself was forced to hastily escape with the remaining army in the steppe. His wife, having heard that the victorious Kiy was already in the city gates, and she, having lost her children, sentenced to separation from her beloved husband, kissed her one-year-old daughter Osnelda goodbye and committed suicide. Little Osneldu Kiy captured.
Although the grown-up girl does not remember either father or mother, she does not forget about her background and hates Kia, a kind of killer. However, the younger brother Kia Horev evokes other feelings in Osneldy. A noble young man who, to the best of his ability, tried to alleviate the burden of a captive-languishing girl, she likes it.
One day Osneldin’s mother, Asgrad, brings the princess a happy message: He died down, went with his army to the walls of Kiev, demands a daughter, and Kiy, not wanting bloodshed, agrees to let Osnelda go ... Asgrad is surprised to see that the girl is not happy. In response, Osneld reveals to her mother her love for Horev. Although she wants to connect with her father, at the same time she understands that the day of meeting with Zavlokh will be the day of parting with her lover. Torn between her daughter's duty and love, she no longer knows whether to have fun or to be sad that the moment is close to breaking up with this city, which for her is “sorrow and comfort meeting and mixture ...”.
In this state of mind, Horev finds her. He comes to say goodbye to Osnelda and, once again expressing his love for her, begs him to answer at least on the last day whether his feeling found a response in her soul. The girl admits her reciprocal feeling, but then asks Khorev to forget her - after all, Osnelda must leave Kiev forever. The young man begs her to stay and become his wife, but she remembers her daughter's duty: how can she marry brother Kia? Horev objects: “And if your father allows us to do this? ..”. Inspired by this hope, the lovers decide to send Zavlokh a letter and ask for permission to marry, which again glorifies the Zavlokh clan and ends the world’s old discord with the world.
Unfortunately, Stalverkh, the first Kiev boyar, having overheard the end of the conversation between the lovers, mistakenly concludes that Khorev, with the help of Zavlokha, wants to take the throne in Kiev himself, and warns Kiy about this. Kiy cannot believe that his brother, his heir, whom he loves as a son, is capable of treason. To test Khorev’s loyalty, he calls his brother and orders him to gather soldiers and go against Zavlokh. Horev objects: why fight and shed blood, if it is possible to end the matter with peace, simply by giving Osneld to his father? But if such is the brother’s command, he, Khorev, will go to battle without reasoning and return with the head of Zavlokh. Cue calms down: Horev is not a traitor.
Hearing the voice of pipes calling the regiments for abuse, Osnelda realizes that they will not give her to her father. Shedding tears, the girl sends Astrada to beg Kia for mercy. But Cue does not heed her pleas. But Horev is already gathering the army ... All hopes are crumbling. Therefore, it is not surprising that when Horev comes to Osnelda, she rains down on him a stream of reproaches. The young man makes excuses: to avoid the order means to incur dishonor, and Horev cannot bear it - death is better. The princess begs her lover to at least spare her father and shed as little blood as possible in the battle. But both still hope that from Zavlokh will come news promising an end to contention.
Alas! In his letter, Zavloh forbids his daughter to love Horev. Osnelda decides to commit suicide, but Astrada at the last minute manages to take the dagger from her pupil.
The siege of the city begins. Horev leads the army and works miracles of courage. However, Stalverkh does not abandon his suspicions. He tells Kiy that, according to his information, one of the former Zavlokhovy subjects was released from captivity by Velkar, the confidant of Khorev, and sent to the enemy camp, after which he was returned. Kiy demands that witnesses be introduced to him, and the boyar brings the prison guard, who says that the prisoner was taken away from him supposedly to the sovereign, and the guard of the city gate, testifying that he let the prisoner go to Zavlou with a letter from Kiy. And since Kiy is still in doubt, Stalverch calls up the slave himself. Kiy promises him freedom if he tells the truth, and the captive admits that Velkar brought him to Osneld, who asked him to take the letter to his father; he did this and brought the answer of Zavlokha, and what was in those letters, he does not know. Slave freed.
Kia's last doubts are dispelled. Enraged, he exclaims: “May I not plunge into hell with a Khorev slave,” deciding to kill himself before his brother does it, but before that, destroying Osnelda, the culprit of all ills.
Presented in front of Kia, Osnelda does not want to make excuses and ask for mercy - she is ready to accept the execution. The princess only ardently convinces the sovereign that Khorev is innocent, and in order to prove this, she reveals to Kia what correspondence she actually had with her father. Kiy says that she will believe her if she presents him with Zavlokh’s letter, but Osnelda cannot do this, because she broke the letter. Then Kiy, squeezing in himself the pity that he against the will against the girl, orders Staller to take her a goblet with poison.
However, soon arrived Velkar brings the news of the victory over the enemy and gives Kia the sword of Zavlokh taken by Khorov. Having received such irrefutable evidence of his brother’s loyalty, the tsar immediately orders one of the soldiers to run to Osnelda and release her, he now agrees even to the girl’s wedding with Khorev. But, unfortunately, the order is late: the princess is already dead.
Meanwhile, Khorev generously invites the defeated Zavlou to forget the past and conclude an alliance, and that one, touched by the nobility of the enemy, agrees to become his friend and give his daughter for him. Hearing this, Kiy is even more terrified of his own mistake. Then news comes that Stalverkh, realizing how terribly he slandered an innocent girl, committed suicide by rushing to the Dnieper. In desperation, Kiy publicly confesses to the murder he committed and begs his brother to subject him to fair punishment.
But Khorev has no idea of killing his brother or depriving him of the throne - after all, neither by this, nor by tears can you ever return a lost beloved forever. The young man asks Kia to restore freedom to Zavloku and let him go with the army from the city, and Zavlokha to take Osnelda’s body with him, to bury him with dignity and write over the tomb: “The girl, who rests in this place, / And in hell with her Khorov, / Whom she loved in this life, - / Horev, depriving her, followed her! ”
With these words, Khorev stabs himself with a dagger.
