• Princess Imogen’s new husband, Posthumus Leonatus, is banished from Britain by his father-in-law, King Cymbeline. After Imogen and Posthumus exchange vows of devotion and tokens of love, Posthumus flees to Rome.
• Grieving over Posthumus’ absence, Imogen spurns the romantic advances of her stepbrother, Cloten.
• The Queen, Cloten’s mother, enlists Cornelius and the doctor’s help to concoct various potions.
• In Rome, Iachimo bets Posthumus that he can tempt Imogen into bed. Posthumus agrees to the bet and Iachimo departs for Britain.
• Iachimo gains Imogen’s trust, but fails to seduce her. Upon his return to Rome, Iachimo tells Posthumus otherwise, showing him Imogen’s bracelet as proof. Certain that Imogen betrayed him, Posthumus sends a letter to their servant, Pisania, telling her to lure Imogen into the Welsh wilderness and kill her.
• Imogen, believing Posthumus to be in Wales, disguises herself as a boy and sets off in pursuit of him with Pisania. 
• Meanwhile, Caius Lucius, an ambassador from Rome, arrives at the British court and demands that Cymbeline pay a monetary tribute to Caesar. At the advice of the Queen, Cymbeline refuses, to which Caius Lucius declares war between Rome and Britain.
• Cloten dresses in Posthumus’ clothes and follows in pursuit of Imogen.
• In Wales, Guiderius and Arviragus, Imogen’s kidnapped brothers, have been living with their abductor/assumed father, Belarius, unaware of their royal origins. 
• Imogen arrives in Wales, still disguised as a boy and assumes the name Fidele. She meets the Welshmen, and they welcome her heartily.
• Cloten arrives in Wales and provokes Guiderius, who decapitates him.
• Imogen takes a potion that the Queen gave to Pisania and appears to be dead. The Welshmen lay her with Cloten’s body and leave to fight for Britain. 
• Imogen wakes to find Cloten’s headless body, which she mistakes for Posthumus. Caius Lucius and her army, on their way to a battle against the Britons, discover Imogen/Fidele weeping over the corpse. Imogen offers herself as Caius Lucius’ page.
• Posthumus returns to Britain with the Roman troops, but switches to fight alongside the British army. He and Iachimo encounter each other in the battle, where Posthumus defeats but does not kill Iachimo. 
• In the face of almost certain defeat, Britain wins the day against the Romans, due to intervention by Belarius, Guiderius, and Arviragus.

 

• Gods, confessions, international relations, and family reunions ensue.