For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
On his way home from Thebes, Duke Theseus of Athens meets a group of lamenting women who beg him to take revenge on King Creon for refusing to allow them to bury their husbands' bodies. Theseus does so, and in the battle takes two Theban cousins, Palamon and Arcite, as hostages. Imprisoned in a tower adjoining Theseus's garden, both knights fall in love with his sister-in-law, Emily.
Act II
Released from prison on the condition that he never return to Athens, Arcite nevertheless re-appears there in disguise as a servant, gaining a position in Emily's household. Meanwhile, Palamon manages to escape from prison. While he's hiding out in a grove of trees, he comes face to face with Arcite, and the two agree to fight a duel over Emily. Theseus, while hunting, comes across the two dueling knights. The Duke orders them to stop their fighting but return to Athens in a year's time with one hundred knights each to fight a joust. The winner gets to marry Emily.
Act III
After a year, the two knights return to Athens with their soldiers. After praying to Venus and Mars, the knights lead their companies into battle. Palamon is captured and loses. On his victory ride, Arcite falls from his horse in a freak earthquake. He dies, but commends Palamon to Emily as a husband. After Arcite's funeral Palamon returns to Thebes. He soon re-appears in Athens to marry Emily at the request of Theseus and his council.