King CYMBELINE (Emmy Rupp) rules over Britain under the protection of Rome (her kingdom must pay tribute to Rome). CYMBELINE learns that her only daughter, IMOGEN (Willa Beidler), has secretly married CYMBELINE’s ward, POSTHUMUS Leonatus (Bek Zehr), a person of low birth, and therefore seen as beneath IMOGEN’s station. Furious with the couple's disobedience, CYMBELINE decides to banish POSTHUMUS from Britain. Before travelling to Italy, POSTHUMUS exchanges their bracelet for IMOGEN’s ring. The exchange is a pledge of trust and love between the couple upon their separation. Before leaving for Britain, POSTHUMUS has a run in with hot-head CLOTEN (Ben Reichenbach), CYMBELINE’s step-son and her chosen husband for IMOGEN.
In Italy, at a party, POSTHUMUS meets some locals and boasts of IMOGEN's faithfulness. A party attendee, IACHIMO (Abigail Greaser), compares the women of Italy and Britain to the countries in general, and challenges POSTHUMUS to place a wager on IMOGEN’s fidelity.
Soon after, IACHIMO travels to the British court to seduce IMOGEN and win the wager with POSTHUMUS, but finds that IMOGEN is indeed true to her spouse. IACHIMO does persuade IMOGEN to look after a trunk overnight.
Meanwhile, the QUEEN (Laura Miller), IMOGEN's step-mother, attempts to annul her step-daughter's marriage to POSTHUMUS. She wants her foolish son, CLOTEN, to wed IMOGEN instead. IMOGEN rejects CLOTEN and seeks the help of POSTHUMUS’s servant, PISANIO (Dali Rodriguez), to keep CLOTEN at bay.
Unbeknownst to IMOGEN, IACHIMO secretly hides in the trunk and gains access to her bedroom. While she is asleep, IACHIMO creeps out to record intimate details of the room and of IMOGEN herself in order to win the wager with POSTHUMUS -- including removing POSTHUMUS's bracelet from IMOGEN wrist. With this “proof” of a conquest, IACHIMO returns to Italy. When IACHIMO presents these details and the bracelet, POSTHUMUS believes that IMOGEN is disloyal. In rage, they succumb to IACHIMO's wager.
Because CYMBELINE has not been paying royalties to Rome, CAIUS LUCIUS (Tobias Garcia) comes as an emissary to demand it. When CYMBELINE refuses, CAIUS LUCIUS declares war on behalf of Rome.
POSTHUMUS sends a letter to IMOGEN telling her to travel to Milford Haven (in Wales) in the hopes of a reunion; but sends a separate letter addressed to their servant, PISANIO, commanding her to kill IMOGEN for her infidelity. The faithful PISANIO does not believe IMOGEN is guilty of any wrongdoing, and in traveling with her to Milford Haven in Wales, reveals the letter sent by Posthumus. PISANIO advises IMOGEN to disguise herself as a boy and sign up to serve in CAIUS’s army. PISANIO then leaves the distraught IMOGEN to seek her fortune and sends word to POSTHUMUS that she has carried out the murder. POSTHUMUS has a change of heart, and is distraught and overcome with guilt upon hearing the news. Meanwhile, angry at his rejection by IMOGEN, CLOTEN discovers that IMOGEN has escaped the court. Wearing a stolen set of POSTHUMUS's clothes, CLOTEN pursues IMOGEN to Wales.
In Wales, IMOGEN (as the disguised 'Fidele') meets and befriends a young hunter GUIDERIUS (Cara Wilson). CLOTEN, traveling separately in the hopes of finding IMOGEN and bringing her back to court, runs into GUIDERIUS, who is annoyed by CLOTEN's arrogance. After a fight breaks out between them, GUIDERIUS beheads CLOTEN. GUIDERIUS returns to her cave and finds Fidele apparently dead. IMOGEN/Fidele has actually taken ‘medicine’ given to her by PISANIO via the QUEEN (IMOGEN’s stepmother). The QUEEN believed it to be a deadly poison. But CORNELIUS (Alex Miller) the doctor who made it for the QUEEN had secretly substituted a sleeping draught after suspecting her motives.
GUIDERIUS mourns Fidele as she places CLOTEN’s body beside Fidele for burial, then heads out to fight for Britain in the war. When IMOGEN/Fidele awakes from her drugged sleep, she finds herself lying beside a headless corpse wearing POSTHUMUS’s clothes. She bewails her fortune and her spouse’s apparent death. At that moment, CAIUS LUCIUS arrives on his way to battle and takes the disguised IMOGEN/Fidele as their page.
GUIDERIUS ultimately helps the British to overcome the Roman invaders. POSTHUMUS originally fights on the British side in disguise. Together, GUIDERIUS and POSTHUMUS save CYMBELINE at a key point in the battle. At the end of the battle, POSTHUMUS changes clothing once again to be taken prisoner with the defeated Romans as penance for killing IMOGEN. In jail, they dream of their dead parents whose ghosts, along with the god Jupiter, leave them a prophetic inscription and the hope that their spouse may yet return.
At the end of the war, CYMBELINE discovers that the QUEEN has died, admitting to her plots and treasons. CYMBELINE condemns the Romans (including IMOGEN/Fidele, IACHIMO, and POSTHUMUS), but CAIUS LUCIUS asks for Fidele’s freedom. When CYMBELINE grants a boon to Fidele, the page asks why IACHIMO wears POSTHUMUS's ring. As IACHIMO admits to deception, POSTHUMUS reveals themself to the court and relates how they arranged IMOGEN's death. IMOGEN reveals herself as Fidele in turn, amazed that POSTHUMUS is alive because she had mistaken the beheaded CLOTEN for her spouse. She demands that IACHIMO apologize and return the ill-gotten bracelet and ring directly to her, not to POSTHUMUS.
Explaining how CLOTEN came to be wearing the clothing of POSTHUMUS, PISANIO tells the story of CLOTEN’s journey to Wales. GUIDERIUS admits to killing CLOTEN. CYMBELINE is angry, but CORNELIUS reveals that GUIDERIUS is CYMBELINE's long lost child, stolen in infancy by CYMBELINE's friend turned banished foe, BELARIUS. With IMOGEN’s long-lost sibling returned, CYMBELINE points out that IMOGEN has lost her inheritance of the kingdom. However, GUIDERIUS abdicates on the spot, having no interest in living according to the dictates of royalty. The characters now see each other in a new light, with forgiveness in the air and a hope for peace. CYMBELINE proclaims that “pardon is the word to all.”