Imogen is still disguised as a boy.
Belarius notices that Imogen/Fidele is not well and asks her to stay in the cave while he and the boys go hunting. Arviragus addresses her as "brother". This has an ironic ring for the audience, which knows that he is Imogen's brother, but not for the characters themselves, who do not know they are related and think it a mere expression of friendship. Guiderius offers to stay with her, but she insists that he go, since she does not want to socialize and he cannot cure her by staying.
Guiderius tells Imogen/Fidele that he loves her as he does his father, though he does not know why. Arviragus says he also loves Imogen, to the extent that, if one among them had to die, he would choose Belarius rather than her. Belarius is not offended by this, taking it as a sign of the youth's inherent nobility that he has noticed something special about Imogen.
Aside to the audience, Imogen/Fidele reflects on the kindness of her hosts, and says that she has been lied to at court, where it is said that everyone outside that place is a savage. Her sickness, she says, is a heart-sickness (for love of Posthumus). She takes the drug that Pisanio has given her.
Guiderius tells his brother that he could not persuade the youth to tell 'his' story. All 'he' would say was that he was well-born, but unfortunate, the victim of dishonesty, but honest. He told Arviragus that he might learn more in future. Imogen retires into the cave.
Belarius comments that the youth evidently has "good ancestors" (line 48). Arviragus is struck by his "angel-like" singing voice (line 48), and Guiderius by his exquisite cooking skills.
Cloten enters. He is upset that he has not found Imogen and Posthumus, and suspects that Pisanio has tricked him by giving him wrong directions. He too feels faint.
Belarius recognizes Cloten as the son of the Queen. Belarius and the boys are viewed as outlaws, and Belarius thinks they should escape. Guiderius decides to stay with Cloten and suggests that Belarius and Arviragus go to search for any followers. Cloten challenges them as they flee and Guiderius is left to answer Cloten, whom he calls a "slave"-a term of abuse. Cloten calls Guiderius a law-breaker and demands that he yield. Guiderius asks why he should. Cloten replies, by his clothes-he may mean that they show he is from the court. Cloten tries to provoke Guiderius with insults, but Guiderius does not rise to the bait because he sees that Cloten is a fool. Cloten tells Guiderius his name, thinking that will make him tremble in awe. But Guiderius says he would be more fearful of something with the name of toad, adder or spider, that is, something that can harm him (it was thought toads were venomous). Cloten tries again, saying he is the Queen's son, but Guiderius says he only regrets that he does not seem worthy of this high position.
Cloten wants Guiderius to fear him, but Guiderius is unmoved, saying that he fears (respects) only those whom he reverences; he laughs at fools. They leave, fighting.
Belarius and Arviragus return, without having found any followers of Cloten. Guiderius comes in carrying Cloten's head. He says that had he not killed Cloten, Cloten would have killed him. Belarius is horrified, but Guiderius is unrepentant. He says the law does not protect them, so why should they allow "an arrogant piece of flesh" (line 127), who usurps the role of judge and executioner, threaten them just because they fear the law?
Belarius says that though he saw no one else, Cloten must have some attendants, whom Belarius fears. He may have come on a dare, to bring the runaway outlaws back, but it is still unlikely that he would come alone.
Arviragus is philosophical, saying that they must accept their fate and that his brother has done well. Guiderius says he killed Cloten with his own sword and plans to throw his head into the river, whence it will be carried out to sea. He will tell the fishes that this is the Queen's son: this is the extent of his care for Cloten.
Belarius fears the deed will be revenged, and wishes Guiderius had not done it. Arviragus wishes that he himself had done it, so that the revenge would pursue him. Belarius warns them not to seek danger where there is no profit.
Belarius reflects that the boys' behavior shows an inherent royal-ness, which they did not need to be taught. He wonders what Cloten's visit will bring in its wake.
Guiderius enters to report that he has thrown Cloten's head into the stream. They are interrupted by the sound of solemn music played on Belarius's instrument. Arviragus is the one who generally plays this instrument, but he has not played it since their mother's death. Guiderius wonders what solemn occasion merits its use.
Arviragus enters with Imogen, seemingly dead, in his arms. He makes an elaborate speech, noting all the different flowers he will plant on her grave. The more practical Guiderius cuts him short, saying that they should bury Imogen near to their mother. Arviragus wants to sing the same dirge that they sang to their mother, but Guiderius says he will not be able to sing for weeping.
Belarius reminds them that they must also bury Cloten, and with royal honors, since he was the son of a queen. Guiderius asks him to fetch the body, though he comments that when dead, a poor person's body is as good as a powerful person's.
Guiderius sings the dirge, "Fear no more the heat o' th' sun" (line 258), which deals with the mutability of all things, which must "come to dust".
After Belarius and the boys leave, Imogen awakes from her drugged sleep in a delirious state. She is shocked into clarity by the sight of Cloten's headless body next to her, dressed in Posthumus's clothes. She hopes that she is dreaming. But when it becomes clear that she is not, she is convinced that Pisanio has conspired with Cloten to murder Posthumus. The fact that Pisanio gave her a drug that proved "murd'rous to the senses" (line 328) confirms his malice. Imogen falls on the body of Cloten.
Lucius enters with some of his captains and a Soothsayer. A Captain reports that the troops that were stationed in Gallia are now at Milford Haven and ready to fight. The "gentlemen" of Italy, commanded by Iachimo, are also sailing for Britain at the next favorable wind. Lucius gives the order to muster the existing troops, then asks the Soothsayer what he has dreamed regarding the war. He replies that he saw Jove's sacred bird, the eagle, winging its way westwards and disappearing into the beams of the sun, which means Rome will be victorious.
Lucius finds the bodies of Imogen and Cloten. The Captain says Imogen is alive. Lucius asks Imogen to explain what has happened, the identity of the headless man, and her interest in him. Imogen, still adopting the persona of Fidele, describes the body as her master, killed by brigands. She laments that she will never find another to equal him. She says his name is Richard du Champ and that her name is Fidele. Lucius says her name fits her faith, and invites her to enter his service. Imogen agrees, and Lucius bids her be cheerful, as "Some falls are means the happier to arise" (line 403). Lucius and his men go to dig Cloten a grave.
Imogen's taking of the drug is another hint, along with the previous references to sleepiness, that a transformation in awareness is about to happen. The regenerative theme is invoked in Arviragus' description of patience and grief as two plants which have taken root in Imogen, and his prayer that the first thrives while the second withers.
Cloten's insistence that Guiderius should know who he is by his clothes shows the excessive importance Cloten gives to appearance over inner identity. Guiderius recognizes Cloten's foolishness for thinking that the borrowed clothes "make" him (line 83). It should be the other way around: men make clothes.
The contrast between the true world of the Welsh countryside and the false world of the court is clear in the fact that in the country, Cloten's and the Queen's names and high rank fail to strike awe into anyone's heart; venomous beasts, on the other hand, can do harm and are feared. The appearance versus reality theme is picked up again in Guiderius' comment that Cloten does not seem worthy of such high birth. Note the deliberate contrast between Cloten, who constantly expected respect on the basis of his superficial rank, but inwardly did not deserve it, and Guiderius, who is outwardly a poor outlaw but who exemplifies princely and noble behavior.
This appearance versus reality theme plays into that of worth. Guiderius, after killing Cloten, calls him a worthless "empty purse" with no money in it (lines 113-4). After Guiderius has cut off Cloten's head, Belarius fears that "the body hath a tail / More perilous than the head." This grotesque image brings home Cloten's bestial nature and is an outward expression of his inward state-all animal appetite with little of the higher reason that in Renaissance thought separated men from beasts.
Guiderius' quip that he will tell the fishes that the head he has thrown into the sea is that of the Queen's son represents Cloten stripped of his much-vaunted nobility and reduced to the base level of food for beasts. This image strips away the sophisticated but false veneer behind which the court has hidden its moral decay. The headless corpse is symbolic too of the kingdom under Cymbeline: he is a weak king ruled by his wife. The entire episode of Guiderius's killing of Cloten has an oddly fable-like quality. It is presented more as a story of a noble knight killing a monster than how it would be seen in a more realistic play-the murder of the heir to the throne on what appears to be trivial provocation.
Belarius likens the two boys to nature herself. He compares their gentleness to a breeze that leaves the violet unmoved, and their roughness to the strongest wind that can bend a tree. He says that though they have never been taught royal behavior and valor, it grows in them as a wild (i.e. not deliberately cultivated) crop. This is another example of the theme of inherent royalty or nobility.
The dirge, "Fear no more the heat o' th' sun" (lines 258-81), is perhaps the best known part of the play. It draws upon the theme of gold and worth, and sets them in the context of the mutability of all things: even "golden lads and girls," those most valued in life, must eventually come to dust, as surely as do chimney sweeps. Death is the great leveler, and makes the "frown o' th' great," "slander" and the "tyrant's stoke," as well as mankind's great achievements in the field of learning and lovers' passion, irrelevant.
Coming so soon after Arviragus' lyrical speech about the flowers he will plant on Imogen's grave, this song has the effect of measuring the world that man constructs for himself and identifies so strongly with, but which all ends in dust, against the great creative force of nature, which endlessly generates new life.
Belarius's comment about dewy herbs being fittest for graves recalls the Queen's sinister words in Act 1, scene 6.
Imogen's invocation of a drop of pity as small as "a wren's eye" (line 305) represents another bird image, part of the theme of regenerative nature. Another example of the bird theme is the soothsayer's dream of Rome's victory in battle as Jove's sacred bird, the eagle, winging its way westwards (line 348).
Cymbeline: Novel Summary: Act 4 Scene 2