Posthumus is talking to a British Lord, who fled the battle. Posthumus says there is no shame in this, since all seemed lost for the Britons, until the gods intervened. He tells the Lord how an old man and two boys-obviously Belarius, Arviragus and Guiderius-turned the battle around by stopping the Britons from fleeing and making them fight the Romans. The Romans are defeated, and Lucius has been taken prisoner.
Posthumus, disappointed that he did not die in battle, has dressed again in Roman clothing. He comes forward and gives himself up to the Britons, wishing to be taken prisoner and put to death. They capture him and plan to take him to the King.
Posthumus commands more sympathy in this scene than previously. Giving himself up to the Britons to be put to death is arguably a just punishment for his actions.
Cymbeline, in another bird image, is compared to a bird without wings (line 5); the Romans are like a predatory animal, "Lolling the tongue with slaught'ring" (line 8). However, the Britons win because the gods help them ("the heavens fought" (line 4). This is one of the play's most notable instances of supernatural intervention-though it is dramatically unconvincing, as is confirmed by the Lord's reaction to Posthumus's account of it-and gives a foretaste of the elements that will follow in the next scene.
Cymbeline: Novel Summary: Act 5 Scene 3