Demetrio e Polibio
Polybius, king of Parthia, protects his daughter Lisinga and her lover Siveno, whom all believe to be the son of a minister. Siveno is actually the long-lost son of Demetrius, king of Syria. Demetrius disguises himself as a messenger to reclaim Siveno, but when he enters the palace, he finds Lisinga alone and kidnaps her instead. Polybius and Siveno demand her release, while Demetrius threatens to kill her unless Siveno is handed over. An old medallion makes Demetrius recognize Siveno as his son. Demetrius reveals his identity, the prisoners are reunited and peace is restored.