Cloten, having arrived in Wales, prepares to execute his ghastly plan against Posthumus and Imogen, while Belarius and his supposed sons leave an ailing Imogen for the hunt. As they part, Imogen, Guiderius, and Arvigarus declare an inscrutable love for one another; they sense the deep bond of their royal siblinghood, though all are as yet ignorant of its true nature. Imogen, "heart-sick" from betrayal and the trials of the wilderness, takes Pisano's drug, which he had received from the Queen, while the men are out hunting. While on the hunt, Belarius, Guiderius, and Arvigarus run into Cloten. Belarius recognizes the young prince from his days at court and thinks that he and his sons must be the object of an ambush. Guiderius sends his father and brother away and confronts Cloten himself. When Cloten insults him vigorously, Guiderius insults Cloten right back; when Cloten swears Guiderius shall be beheaded for his impudence, Guiderius-ever the man of action-cuts Cloten's head off.
As the three rustics return to their cave, Belarius is convinced that Guiderius's slaying of Cloten will be the end of them. This concern recedes, however, when they come upon the apparently dead body of "Fidele"-i.e. Imogen. The Queen's potion, just as Cornelius had promised, has indeed cast upon her the appearance of death. They eulogize over Imogen's body and sing a dirge, then lay her out on a flowerbed, near which Guiderius has placed the beheaded body of Cloten. As soon as they have left, Imogen awakens. She recognizes the clothes Cloten is wearing as Posthumus's, and assumes that Pisanio and Cloten have conspired to poison her and then torment her with the dead body of her beloved. Grieving, she weeps over the body she assumes to be her lover's.
Just then, Lucius and his troops enter the same pasture. Philarmonus, the soothsayer, prophesies a Roman victory in the coming battle. Then Lucius comes upon Imogen and Cloten. He is hugely impressed by the devotion that Imogen-who is still calling herself Fidele-displays for her beheaded love, whom she declares is her dead master, calling him "Richard du Champ." He determines to take this loyal page as his own, and Fidele follows him as he prepares for war.
Meanwhile, in Cymbeline's court, the Queen has taken ill following the news of her son's disappearance. Cymbeline's dying Queen distracts him from preparing for the approaching battle with Rome, and Pisanio notes that he hasn't heard from either Cloten or Posthumus, whom he has told of Imogen's death and whom he has sent a bloodied cloth as proof.
Back in Wales, Guiderius and Arvigarus argue with Belarius, who insists that they should flee into the wilderness before Cloten's body is discovered. The twins say that they will fight for Britain in the coming battle instead, driven by their innate nobility to engage in conflict. Belarius finally agrees to accompany his sons, hoping that his agedness will hide his identity from those who might recognize him in the British army.
The analysis of Act Three concluded with the observation that no one recognizes Imogen to be a woman simply because she wears the clothing of a man. Yet some nevertheless recognize something essentially-rather than superficially-compelling in Imogen: her royalty. Her brothers, who are also disguised royals, feel an instinctual (and, confusingly, somewhat erotic) love for her that overwhelms their love for the man they think is their father. This love contrasts with their immediate impression of another prince, Cloten, whom they declare to be false and whom Guiderius has no compunction about killing in Act Four. Imogen, Guiderius, and Arvigarus, as the right-born royals in the play, know Cloten to be an imposter without actually knowing it, just as they know one another to be virtuous without being aware of each other's true identities.
Royalty announces itself not only in this sibling bond, but also in the very natures of Guiderius and Arvigarus. Taken at face value, these characters are absurd: they have never lived outside of the forest, have never known company besides that of each other and their supposed father and mother. Even granted that Belarius was once a high-ranking court official, there is no way that they could have realistically developed the high speech, refined social sensitivity, or royal bearing that both of them demonstrate. Of course, as is consistently apparent in Cymbeline, common-sense is not particularly vital to the plot. Guiderius and Arvigarus behave royally simply because they are royal. Their understanding of their royalty has nothing to do with being royal-the being trumps the understanding. They are the extreme opposite of Cloten, who expected the world to recognize his importance because of the clothes he wore. The twins wear the clothes of peasantry, yet act the part of royalty because their genetics trump their upbringing.
This unstoppable virtuousness spills over, in the Act's end, into their comportment on the battlefield. As Belarius says, "The time seems long, their blood thinks scorn / Till it fly out and show them princes born." The disguised princes obey no law but that of their blood-instinct dictates that they kill Cloten and long for battle. Self-preservation does not enter into the equation except at the farthest remove of destiny: because their blood will "show them princes born," they throw themselves into the fray. What would be incredibly stupid actions in anyone else-killing a prince and then fighting for the prince's side in war-in this case are revealed as the workings of divine fate.
Imogen, for her part, has perhaps her finest moment in the whole play when she mourns over the body of the man she thinks is Posthumus. This situation, more than any other, captures the absurd beauty of Cymbeline. Keep in mind that Imogen consistently-almost obsessively-refers to Cloten's dead body as that of Posthumus, that a headless corpse on stage is the object of an impassioned eulogy, that Imogen has herself been absurdly left for dead on a bed of flowers, then inexplicably abandoned just before she wakes up, and that given all of these absurdities, the scene remains deeply moving.
J.M. Nosworthy, writing of the scene in the Arden edition, writes, "Shakespeare resolves the complexities with facetious grace liberating the spirit of comedy into what is ostensibly a tragic period and allowing Imogen's half-conscious thoughts free play." In other words, Imogen experiences the scene as pure tragedy; the audience, knowing the body to be Cloten's, experiences it as farce. The facts render the scene ridiculous, yet Imogen's naive pathos makes it moving. These old audience reactions-ridicule, empathy, etc.-combine to make something new, some absurd mingling of reactions. Indeed, perhaps this scene expresses something new to Shakespeare, even something new to the dramatic genre, but something familiar to human beings-it conveys the inherent ambiguity of different perspectives on a given situation. Imogen's perspective is not the audience's, yet both views are equally valid.