Xerxes, the King of Persia, resolves to marry Romilda. However, Romilda is also loved by Arsamene - the brother of Xerxes. Meanwhile, Atalanta is in love with Arsamente. Amastre, Xerxes fiancé whom he has abandoned, disguises herself as a man and seeks revenge. Atalanta's pretence that Arsamene really loves her and the insistence of Xerxes on marrying Romilda cause a series of complications, enlivened by the comic servant Elviro. Eventually, all is resolved when Xerxes reunites with Amastre and Arsamene reunites with Romilda.