After a prologue which shows several aerial views of the Acropolis, the story begins. The friendship of Damon, the senator, and Pythias, the soldier, is famous in Ancient Syracuse. Because the general Dionysius is infatuated with Calanthe, Pythias' sweetheart, he sends the soldier to fight the Carthaginians at the Battle of Agrigentum. Pythias returns in triumph, and then angers Dionysius even further when he defeats Aristle, the general's favorite, in a chariot race. During the wedding ceremony for Pythias and Calanthe, Dionysius has himself proclaimed sovereign while Damon is absent from the Senate. Shocked, Damon attempts to assassinate Dionysius, but he fails and is sentenced to death. In order for Damon to say goodbye to his wife and son, Pythias leaves Calanthe and takes his friend's place in prison, offering to die in Damon's place if he does not return. Despite several tests of the strength of their friendship, they remain loyal to each other and so impress Dionysius that he allows them both to go free.