The Prince of Parthia is a Neo-Classical tragedy by Thomas Godfrey and was the first stage play written by an American to be presented in the United States by a professional cast of actors, on April 24, 1767, at the Southwark Theatre in Philadelphia.

The plot then moves into Act Two; when Vardanes and Lysias hear Arsaces tell Bethas that he loves Evanthe, they decide to tell King Artabanus that Arsaces is a traitor for sympathizing with Parthian enemies.

By the time the plot reaches Act Three, Thermusa is very angry because she knows King Artabanus is lusting after someone else.

She tells this to Vardanes, who decides to use this to destroy Arsaces and take the throne of Parthia for himself.

Phraates tells Gotarzes that he overheard Vardanes and Lysias talking about how they killed King Artabanus in his sleep.

Thermusa enters the prison to kill Arsaces, but she sees a bloody ghost of King Artabanus, which causes her to “brain” herself against the wall, committing suicide.

Then, a huge battle occurs, pitting Vardanes, Lysias and all of their followers against Arsaces, Barzaphernes, Phraates, Gotarzes and their men.