Summary
Lucius, Iachimo and the Roman army enter at one side of the stage, and the British army at another, with Posthumus following, dressed as a poor soldier. There is a skirmish between Iachimo and Posthumus, who disarms Iachimo and leaves. Iachimo, left alone, is penitent that he slandered Imogen, the princess of Britain, and says that his guilt is robbing him of his courage. Otherwise, how could this poor soldier have subdued him, a professional soldier?

The battle continues. The Britons retreat in disarray and panic, and Cymbeline is taken prisoner. Belarius, Guiderius and Arviragus enter and, helped by Posthumus, rescue Cymbeline. Then Lucius, Iachimo and Imogen enter. Lucius sends Imogen away from the fighting, for her safety. Iachimo warns Lucius that the British are bringing in reinforcements. Lucius says they too must bring in more troops, or retreat.

Analysis
Coming fast on the heels of Posthumus' penitence is Iachimo's. Both are perhaps less rewarding and dramatic than they should be, since we do not see the journey that led them to this point.

The decay into which Cymbeline's kingdom has fallen is clear from the shameful disorder into which his army descends. The fact that his lost sons become his rescuer emphasizes the regenerative theme of the new world redeeming the old. The cure for the court's and the nation's sickness lies in the sons' hands. Belarius's involvement is satisfying, since it expiates his sin of stealing the royal children: he heals where once he wounded.