Both the emperor Xerxes and his brother, Arsamene, are in love with Romilda, who favors the latter. Atalanta, Romilda’s sister, in love with Arsamene, resolves to help Xerxes, reasoning that Arsamene may choose her if he is denied Romilda. To complicate matters further, Amastre, to whom Xerxes was once betrothed, has disguised herself as a man in order to observe the king.
When Romilda rejects Xerxes, the scorned king has Arsamene banished. Atalanta intercepts a letter from Arsamane to Romilda and spreads a series of falsehoods in an attempt to drive a wedge between the couple; however, Romilda and Arsamene’s love never falters.
Xerxes tells Ariodate, Romilda’s father, that his daughter is to marry “a man of Xerxes’ lineage.” Although Xerxes means himself, Ariodate assumes the bridegroom will be Arsamane, the king’s brother. When Arsamene and Romilda arrive and learn of the king’s decree, they immediately wed, astonished. Moments later, Xerxes arrives, furious.
Amastre, still in disguise, asks the king if he would like to see the death of the betrayer, the one who, despite being deeply loved, left in pursuit of another. When Xerxes agrees, Amastre reveals her identity. Xerxes, ashamed, asks her to kill him, but she refuses, and the two are reconciled.
Synopsis used courtesy of Kelley Rourke/The Glimmerglass Festival