The opera is set in the 4th century BC in Phoenicia.
Aminta is heir to the throne of Phoenicia, who was deprived of his title in infancy. He is ignorant of his legacy and lives in the country as a simple shepherd. He is happy and looks forward to his wedding with his beloved and noble bride Elisa. Elisa brings him the news that Alessandro the Great (that is Alexander of Macedonia) has liberated Aminta’s native city of Sidon and deposed tyrant Stratone. He now wants to find the rightful heir to Sidon. Alessandro himself, accompanied by his Phoenician friend and advisor Agenore, soon comes to Aminta. After their meeting with Aminta, both are convinced that the shepherd is indeed Abdalonimo, the lost heir to the throne of Sidon they have been looking for all along.
Tamiri, who is the daughter of a previously deposed tyrant, finds shelter with Elisa. Agenore recognizes his beloved princess, who is disguised as a shepherdess. He wants to defend Tamiri before Alessandro. Agenore tells Aminta that he is the rightful heir to the previous king and will get the throne of Sidon. Elisa and Aminta are happy, but scared they will not be able to marry.
Elisa hurries to Alessandro’s camp to find her lover, but Agenore stands in her way. He tells her not to distract the king. Aminta is also not allowed to see his beloved Elisa as now the affairs of his kingdom should come before romantic feelings. Aminta grows to understand that his title deprives him of liberty. He cannot imagine his life without Elisa.
Agenore informs Alessandro that the late tyrant’s daughter is alive. Alessandro wants to marry her off to Aminta. Agenore can hardly hide his true feelings, but he does not want to stand in the way of his beloved Tamiri becoming the queen.
Both women are in despair: Elisa does not want to lose Aminta, while Tamiri cannot live without Agenore. Both try to persuade Alessandro to change his mind. However, he remains adamant.
Everything is set for a wedding at the Temple of Hercules. Alessandro’s plans threaten to destroy the happiness of four people. Aminta, now dressed in his old shepherd’s clothes, proclaims that he would rather refuse the throne than lose Elisa. Alessandro is touched by this and gives his blessing to both couples, who will rule Sidon together.