Act I
At his camp in Belgrade, Suleiman the Magnificent draws up plans to conquer Vienna. The Ottoman Sultan is at an advanced age and ignores his doctor’s warnings regarding his poor health. The only obstacle on his way to Vienna is the fortified town of Szigetvár, which is defended by the Croatian governor Nikola Šubić Zrinjski. The grand vizier Mehmed Sokolović advises the Sultan to try and bypass Szigetvár altogether due to Zrinjski and his soldiers’s renowned bravery. But Suleyman is sure he will be victorious and orders the march on the fortified town.
In Szigetvár, Zrinjski’s daughter, Jelena, meets with Lovro Juranić, a warrior who is preparing for the upcoming battle. Jelena confides in her mother, Eva, telling her that she fears for Juranić’s life. They are joined by Zrinjski, who informs the family that the Ottomans are on the march. Juranić asks Zrinjski for Jelena’s hand in marriage. The father gives his consent, promising that the wedding will take place after the Ottomans have been defeated.
With Szigetvár under siege, Zrinjski’s soldiers ready themselves for the decisive battle. The warrior Gašpar Alapić advises Zrinjski to send his wife and daughter somewhere safe until the danger is over. But Eva is adamant that Jelena and she will stay there with their loved ones. Zrinjski has been urged by the Holy Roman Emperor to defend Szigetvár until help arrives. His soldiers all take a solemn oath to defend the fortified town to the last man.
Act II
At the Ottoman camp, celebrations take place to mark the fortieth anniversary of the Battle of Mohács. Suleyman is impatient because of Zrinjski’s resistance and sends Sokolović to Szigetvár with a message warning Zrinjski to surrender.
Zrinjski senses that he will not be able to hold off the enemy for much longer. The grand vizier arrives and offers Zrinjski the Croatian crown in exchange for his surrender, but threatens to torture his son should he refuse. The governor orders that the outskirts of the fortified town be abandoned and set on fire, then he sends Sokolović back with the message that Suleiman can enter the town himself if he dares.
Act III
The Sultan has died from natural causes. Sokolović keeps his death a secret from the Ottoman troops and orders another attack on Szigetvár.
Eva has brought Jelena to an underground room in the fortress to protect her from the approaching soldiers. The daughter can only dream of Juranić, who suddenly finds her in her hiding place. Jelena asks him to kill her, fearing that she will otherwise fall into the Ottomans’s hands. Juranić grants her wish, giving her a final kiss before stabbing her with his sword.
As Eva and Zrinjski say goodbye to each other, Juranić brings them the news of Jelena’s death. Eva sets the fortress on fire and the soldiers all head into the final battle. Szigetvár falls.