When ambassador from Rome, Cauis Lucius, urges Britain to resume paying her tribute owed Augustus Caesar which had been neglected of late, Cloten and his mother justify the neglect by respectively boasting of Britain’s new found might and disparaging Julius Caesar’s original attempt to conquer Britain as something less than triumphant. Cymbeline urges Cloten to let his mother do the talking, but Cloten rattles on. He welcomes Lucius to Britain, echoing Cymbeline who had done so after informing Lucius that Britain will oppose Rome at the risk of incurring Rome’s wrath as Britain is a proud people who account themselves no less warlike than Rome’s current adversaries, the Pannonians and the Dalmatians.
Pisanio is incredulous as he has received a letter from Posthumus, urging him to kill Imogen. Posthumus claims that Imogen has made a cuckhold of him. Pisanio is certain that a dastardly Italian has abused Posthumus and resolves not to follow through on this obligation. He does hand Imogen a letter, however, the contents of which falsely asserts that Posthumus has returned to Britain, to Milford-Haven, Wales. Though Pisanio does his best to discourage Imogen from exulting at the false news (Pisanio is to kill Imogen at Milford-Haven as per Posthumus‘ instructions), she is exactly that exultant, and is only eager to get to Milford-Haven as fast as she can.
In a remote cave, in the wilds, Morgan exhorts Polydore and Cadwal to wake up and perform their morning exercises, arguing that the simple, unadorned life that they lead in nature is nobler than civilization which is full of riches and corrupt politics. Polydore and Cadwal argue, however, that they regret knowing nothing about civilization, suggesting that they would not mind getting a taste of life in civilizationt if only to see for themselves what that life is like. Morgan can only insist that civilization is full of lies, deceit, and hypocrisy, and to prove it he points to his own life as exhibit A. He had been a renowned soldier in Cymbeline’s army with a dazzling, promising future ahead of him when two conniving villains managed to get him banished by convincing Cymbeline that he--Morgan--was secretly in league with the Romans. It’s a story that Polydore and Cadwal have heard before, and satisfied for now they leave to perform their morning exercises.
Meanwhile, Morgan reveals to the audience the entire story of which Polydore and Cadwal are ignorant. Polydore’s and Cadwal’s real names are Guiderius and Arviragus. They are Cymbeline’s sons who were abducted when they were babies by Morgan as a way to get back at Cymbeline for unjustly banishing him. Having grown up in Morgan’s care, Polydore and Cadwal believe Morgan to be their father. Morgan’s real name, by the way, is Belarius.
Having arrived at the precincts of Milford-Haven, Imogen is anxious to meet Posthumus when Pisanio shows her the letter wherein Posthumus orders Pisanio to kill Imogen on the grounds that she has betrayed Posthumus. Cursing her fate, Imogen urges Pisanio to get on with it and kill her. She is sure that Posthumus, thinking that she has been unfaithful, has been consorting with prostitutes, and to teach him a lesson she is determined to have herself killed and thereby have Posthumus lament his loss when the truth eventually comes out. Pisanio refuses to carry out Imogen’s command, prompting Imogen to ask then why has Pisanio taken the trouble to carry out the first phase of Posthumus‘ plan, i.e. remove her to Milford-Haven and away from Cymbeline’s court, if not for the purpose of killing her in a out-of-the-way site. Pisanio explains his counter plan in which Imogen is to give the impression that she has been slayed. Having made Posthumus believe that she is dead, Imogen is to disguise herself as a man and offer her services to Caius Lucius who is scheduled to make a brief sojourn at Milford-Haven. If all goes to plan, she will be in Rome, serving as Caius Lucius’ attendant which would allow her to keep tabs on Posthumus. Imogen likes the plan and determines to undertake it immediately. Pisanio hands her a box of medicine (the one given him by the Queen) in case she gets sick, and hurries back to Cymbeline’s court.
Having resolved not to pay any tribute to Augustus Caesar, Cymbeline bids Caius Lucius, who will return to Rome via Milford-Haven, a fond farewell. The Queen is praising the King’s resolution when the King, taking note of his daughter’s conspicuous absence, dispatches a messenger to go and fetch her. By and by, the messenger returns to say that Imogen refuses to answer and that her door is barred, prompting the King to go to his daughter himself. Cloten follows the King, at the Queen’s behest. Alone, the Queen confides the audience. She hopes that Imogen and Pisanio will both die, the latter from the box of poison that she had made him a gift of and the former from the dangers that are bound to come her way if she has gone in search of Posthumus. Cloten returns to tell the Queen that Imogen has fled and that the King is in a state of great distemper. He urges her to go and console him. She goes, confiding to the audience that she would like nothing better than to see the King die from his grief. Alone, Cloten is expressing his feelings of love and hate for Imogen when Pisanio appears. He demands Pisanio of Imogen’s whereabouts. Pisanio shows Cloten the letter in which Posthumus informs Imogen that he will be in Milford-Haven, inspiring Cloten to contrive the following plan: He will go to Milford-Haven dressed in one of Posthumus’garments, and there having killed Posthumus will ravish Imogen and then drag her back to Cymbeline’s court.
Though Milford-Haven seemed near when she had parted with Pisanio, Imogen, now disguised as Fidele, has spent two whole days on the road and still there’s a distance to go. Famished, she/he enters a cave where there is food, but no one to claim it. By and by, Morton, Polydore, and Cadwal return from their hunt only to find Fidele feeding on their food. Fidele assures them that he had no intention of stealing and offers them gold for the portion that he had eaten. They refuse the offer and extend their hospitality, welcoming Fidele to partake of their food and to take shelter for the night in their cave. In return, they only require that Fidele tell them his fascinating story.
Two Roman Senators and various Tribunes discuss what is to be done with regards state affairs as per the Emperor’s orders. Because the common men are busy fighting the Pannonians and Dalmatians, the gentry will see to the affairs in Britain by giving their support to the army in Gallia which will be led by Caius Lucius.