King Cymbeline's new Queen, has made the king her puppet and wishes her son Cloten to marry the king's daughter Imogen.
Smooth-tongued Italian named Iachimo, believes all women to be unchaste, and wagers with Posthumus that he will be able to seduce Imogen. After traveling to the British Court and failing in his initial attempt to convince the princess to sleep with him, Iachimo reverts trickery by hiding in a chest and has it sent to her room, observes her sleeping, and steals a bracelet that Posthumus once gave to her.
Imogen flees, becomes lost in the wilds of Wales, and she comes upon a cave where Belarius and his two sons, Guiderius and Arviragus live. The two young men are Cymbeline's long lost sons and are ignorant of their true parentage.
While pursuing Imogen, Cloten comes across Belarius and his sons and fights them.