Cymbeline is King of Britain; his first wife died, and he married a wicked queen. Imogen, Cymbeline's daughter is in love with Posthumus, but her stepmother wants Imogen to marry Cloten, the queen's son. When Imogen balks and secretly marries Posthumus, the king has him banished. Before his departure, Posthumus gives Imogen a bracelet, and she gives him a ring. Posthumus arrives in Rome, where he brags of his wife's beauty and fidelity. When Iachimo questions this, he and Posthumus propose a wager that Iachimo can't seduce Imogen. Iachimo hastens to Britain, where he is rebuffed several times by Imogen. Meanwhile, the malicious stepmother has arranged for her physician to create a poison for Pisanio, a servant and friend of Posthumus. The physician, distrustful of the wicked queen, prepares instead a type of sleeping potion. This is given to Pisanio.
Iachimo, still striving for Imogen, is nothing if not crafty. The rogue hides in a chest carried into Imogen's room, then steals her bracelet while she sleeps. He also takes note of a mole not easily seen. Armed with detail and her bracelet, Iachimo tells Posthumus that he has won the bet, whereupon Posthumus gives up the ring that Imogen gave him. Posthumus, considerably peeved at Imogen, sends a letter to Britain instructing Pisanio to kill her for him. Pisanio instead warns Imogen of the anger of Posthumus, and Imogen flees Cymbeline's court disguised as a page. He also gives the potion, which he believes is a "sovereign restorative," to Imogen. While this is happening, Cymbeline angers Lucius, a Roman ambassador to the point that Rome declares war on Britain over an unpaid tribute to Caesar.
Imogen, in the meantime, gets lost and encounters Belarius, a banished noble who kidnapped Cymbeline's two sons (Guiderius and Arviragus) as infants twenty years before. Imogen, still disguised as the page Fidele, is invited to stay with them. Cloten, however, soon appears on the scene; disguised in Posthumus's clothes, he is on the hunt for Imogen and Posthumus (who he believes to be in Milford Haven). There he encounters Guiderius, who slays Cloten after being insulted. He then cuts off Cloten's head and tosses it into the river. Meanwhile, Imogen has been feeling ill and has taken the Queen's potion, which has made her seem dead. Belarius and the sons lay her beside Cloten's dead body, which, being disguised, is mistaken by Imogen for Posthumus when she awakens, and promptly faints. When she recovers, the despairing Imogen (still disguised as Fidele) accepts service as a page with Lucius (who happens by as she comes to).
Meanwhile, the war continues, and at the court of Cymbeline, the Queen has begun to go mad from the disappearance of Cloten. Posthumus has returned with the invading armies, but disguises himself as a Briton with the hope of dying in battle against the invaders. However, with the aid of Posthumus, Belarius, and the two brothers, the Britons win a glorious battle. Posthumus is later captured and thrown into prison, mistaken for a Roman. There he has a strange prophetic vision. Likewise, Iachimo, Lucius, and Imogen (Fidele) are captured and brought to Cymbeline. The Queen, her condition worsening, confesses her evil doings on her deathbed before expiring. In the ensuing confessions that follow, Iachimo confesses to stealing the bracelet and lying, Posthumus reveals his own identity, Pisanio admits his part in helping Imogen escape, Belarius admits to kidnapping the two boys, and Posthumus and Imogen are reunited and allowed to stay married. A soothsayer interprets Posthumus's vision as the rejoining of Cymbeline's family (which has happened). Finally, Cymbeline releases his prisoners and comes to peaceful terms with Rome.
- Cymbeline, King of Britain
- Cloten, son of the Queen
- Posthumus Leonatus, husband of Imogen
- Belarius, banished lord; disguised as Morgan
- Caius Lucius
- A French Gentleman, friend of Philario
- A Roman Captain
- Two British Captains
- Two Lords, two Gentlemen of Cymbeline's court
- Two Jailers
- Queen, wife of Cymbeline
- Imogen, daughter of Cymbeline by a former queen
- Helen, a lady attendant to Imogen
- Lords, Ladies, Roman Senators, Tribunes
- A Soothsayer
- A Dutch Gentleman and a Spanish Gentleman
- Musicians, Officers, Captains, Soldiers
- Messengers and Attendants