Philaster grew up expecting to become the king of Sicily. After all, he was the rightful heir to the throne. All that appeared to be crumbled before the deposition of his father and the usurpation of his father’s monarchy by the King of Calabria. Although quite the tyrannical despot and not typically given to acts of charity or kindness purely for the sake of acting kind or charitable, the King of Calabria spares the life of the rightful heir, Philaster.
He does so not because of kindness or charity, however; the people of Sicily manifest enough love and support for Philaster that the King of Calabria realized sparing his life was just the politically correct thing to do.
Even more politically correct is the usurping king’s plan to marry off his daughter Arethusa to a very creepy prince from Spain named Pharamond. Just one problem here: Arethusa already loves someone else. That someone else just happens to be none other than Philaster. In order to communicate secretly behind the back of her father the king, Arethusa enlists the assistance of Bellario, Philaster’s page.
Pharamond, being the creepy Spanish prince he is, cheats on his intended with an equally promiscuous lady-in-waiting named Megra. When Arethusa learns of this assignation, she immediately has them arrested with the intent of discrediting Pharamond so that her father will come to his senses about trying to marry her off to a Spanish creep. Megra realizes that her best defense is launch an offense and accused Arethusa of carrying on with Bellario, Philaster’s page.
This lie about his beloved is related to Philaster by Dion, the father of a girl named Euphrasia who also happens to be in love with the rightful heir to the throne. The lie becomes the final straw for those seeking to revolt against king and results in a mob rising to apprehend both Pharamond and the usurping king. Philaster then brings about peace through persuasion as the king returns to Calabria and his right of succession to the throne is reinstated.
Pharamond’s return to Spain with his honor reinstated and full access to Megra produces the play’s most unexpected twist of events. Megra’s accusation of Arethusa being sexually involved with Bellario is undone by the revelation that Bellario is none other than Euphrasia—the daughter of Dion in love with Philaster—in disguise. That, however, is not the final twist. Euphrasia rejects an offer for marriage of convenience in order to accept Arethusa’s offer that she remain on staff as a servant for both her and Philaster.