Here is a short plot summary of The Two Noble Kinsmen:
Duke Theseus of Athens is marrying the Amazon queen Hyppolyta. Immediately after three queens petition him to wage war on Thebes. Its king, Creon has deprived their husbands of proper burial rites.
Two Thebian cousins, Palamon and Arcite decide to join their uncle, Creon’s campaign to defend Thebes, even though they hate Creon, who is an unpleasant tyrant. They perform heroically in the battle but Theseus is victorious. The cousins are imprisoned in Athens, and from their prison they see Hippolyta’s sister Emilia passing by. Both fall instantly in love with her.
Arcite is set free but rather than return to Thebes he disguises himself and stays in Athens. With the help of the jailor’s daughter, who has fallen in love with him, Palemon, he escapes. The cousins meet each other and decide together that they must fight each other to the death with the winner having the love of Emilia. Theseus discovers them and asks Emilia which of the two she wants but she is unable to decide. He decrees that there is to be a jousting tournament and the winner will marry Emilia. The loser will lose his head.
Before the tournament starts all three principals go to the temples of their particular favourite gods. Arcite prays to Mars, the god of war; Palemon to Venus, the goddess of love and Emilia to Diana, the huntress, goddess of virgins, asking her to give victory to the one who loves her best. Arcite wins and Palemon is to be executed. However, before that can happen Arcite is thrown from his horse and killed. As Arcite is dying he bequeaths Emilia to his cousin.