Act I

The Holy Roman Emperor, Henry VI of Hohenstaufen, is preparing to acquire by force of arms the succession to the throne of Sicily after the death of Prince Tancred. In a gathering before the expedition he confirms the decree of banishment from the Empire of the rebel, Henry the Lion, duke of Braunschweig, and all his kin. His wife, Ermengard, pleads with him, reminding him that their daughter, Agnes, has been promised in marriage to the youth Henry, Henry the Lion’s eldest son, but to no avail. Nor does the intercession of the Duke of Burgundy, the French ambassador, serve to change the Emperor’s mind. A short while later the young Henry himself appears, disguised as a troubadour. He begs his friend Philip, the Emperor’s brother (who has quickly seen through the disguise), to help him to see Agnes again, but Philip informs him that the French ambassador has actually come to ask for Agnes’ hand in marriage to the king of France. Nevertheless, the young Henry manages to meet with Agnes, but their passionate encounter is interrupted when news are received that Henry the Lion is marching his troops against Emperor Henry VI. The latter, invoking Henry the Lion’s defiance of the ban, declares the promise of marriage between Agnes and the young Henry to be no longer valid, and he promises his daughter’s hand to the King of France. In a dramatic finale, the young Henry offends the Duke of Burgunday and is arrested.

Act II

The princes faithful to the young Henry rush to his aid, and the Emperor Henry is forced to give up his plan to punish with the young Henry’s death the violation of the decree. He nevertheless gives permission for the Duke of Burgundy, who has been insulted by the young Henry, to fight a duel with the latter, hoping to thus have his revenge. But his wife, Ermengard, on her own initiative and with the complicity of the bishop, has Agnes and the young Henry’s marriage celebrated. When the Duke of Burgundy appears, the young Henry is ready to fight with him; the French knights surround him. but the bishop imposes a truce.

Act III

In a square in Mainz, decked out for celebration, Philip of Hohenstaufen, the Emperor’s brother, takes the young Enrico’s place and challenges the Duke of Burgundy to a duel; but Henry draws his sword and rushes against the ambassador. At the same moment Henry the Lion appears, heavily masked by his visor. The duel goes in the young Henry’s favour: he wounds the ambassador. But the ambassador is revealed to be none other than the King of France himself, who wanted, in disguise, to win Agnes’ love. The young Henry is in a quandry: the king had on one occasion saved his life, so the reason for the duel lapses. At this juncture Ermengard reveals that Agnes and Henry are already wedded in the eyes of God. The Emperor is furious and insists on Henry’s death. But the latter’s father, Henry the Lion, runs to his son’s rescue: he reveals his true identity and, kneeling at the Emperor’s feet, he offers him his sword in subsmission. The Emperor then grants Agnes’ hand to the young enryHenry, while the chorus looks forward eagerly to the expedition for the throne of Sicily.