Cymbeline, who is King of Britain is a widower and has since married a wicked queen who wants her stepdaughter, Imogen, Cymbeline's daughter, to marry her son Cloten.

Imogen will have nothing to do with Cloten as she is in love with Posthumus, whom she secretly marries. Just before the king has Posthumus banished, he gives Imogen a bracelet and she in turn gives him a ring.

When Posthumus arrives in Rome he brags of Imogen's beauty and fidelity and offers a wager to his friend Iachimo.

He bets Iachmo that he can't seduce Imogen.

So off Iachimo goes to Britan to try and seduce Imogen but is rebuked at each of his attempts. Meanwhile, the queen is still scheming and arranges for a poison to be given to Pisanio, who is one of Posthumus's friends and servants. Instead the physician only creates a sleeping potion that is given to Pisanio.

Trying to still win the bet, Iachimo sneaks into Imogen's room in a chest and steals her bracelet while she sleeps, he also glimpses a mole that is usually hidden under clothing. With these two items, Iachimo convinces Posthumus that he has won their wager.

Heartbroken and angry, Posthumus takes off the ring Imogen has given him and sends word to Pisanio back in Britain to kill Imogen.

Pisanio does not kill Imogen, he warns her of the danger and of Posthumus's plan, so disguised as a page, Imogen sneaks out of Cymbeline's court with the potion that was made for Pisanio.

Elsewhere, Cymbeline angers a Roman ambassador to the point where Rome declares war on Britain. Free of the court, Imogen gets lost and encounters Belarius. Belarius is a banished noble who kidknapped Imogen's two brothers, Guiderius and Arviragus, as toddlers, 20 years earlier. Still disguised as the page Fidele, Imogen is invited to stay with them.

In pursuit of Imogen, and Posthumus, whom he believes to be hiding in Milford Haven, Cloten soon arrives dressed in Posthumus's clothing where he happens upon Guiderius, who kills him. Guiderius, insulted by Cloten, cuts off Cloten's head and tosses it into the river.

Imogen, who seems near death because she has taken some of the queen's potion is laid beside Cloten's body, which is still dressed like Posthumus and is unfortunately mistaken by an awaking Imogen for her husband.

When she awakes for a second time after fainting, although still disguised as Fidele, accepts service as a page by a man named Lucius who is walking by as she awakens.

By this time, the queen is mad with worry over the disappearance of her son, Cloten. Also Posthumus has returned to Britain with the invading armies but disguises himself as a Briton in hopes of dying in battle.

Instead of dying however, Posthumus is captured and thrown into prison because he is thought to be a Roman, which is where he has a prophetic vision.

The happy ending of this play begins with the capture of Iachimo, Lucius and Imogen who are brought before Cymbeline. The wicked queen is on her deathbed and admits all of her wrong doings before she dies.

Iachimo also makes his confession and admits to stealing the Imogen's bracelet and lying and Belarius admits to kidnapping the two boys.