A swineherd comes to Emer, his mother, who is making clothing, and says that he does not need to watch the road anymore. Emer throws down her web, and raises her hands reddened with dye and cries out loud.
She asks him what if his master comes home triumphant, why would he be afraid? He is too strong to idle away his life as a swineherd.
He asks where he can find his father, and she says in the Red Branch camp. Cuchulain lives among these men, and even King Conchubar sings his praise. Cuchulain notices that the swineherd has invaded their camp, and fights the young man - his son, though he does not know that - remarking that the stranger looks like a woman he once loved.
As Cuchulain kills the swineherd, the youth reveals that he is Cuchulain's son. Cuchulain is so full of grief and rage that King Conchubar is afraid that he will slaughter them all. He asks the druids to chant ancient spells into Cuchulain's ears, so that when he arises, enraged, he will fight the sea rather than humans.
Although Yeats writes poetry that is lyric in form, the subject matter of this piece is epic, in the style of Homer or the ancient Irish bards. It has a clear narrative with a beginning, middle and end. The poem enacts a familiar Oedipal struggle. Instead of the son slaying his father, as is the case in the Oedipus myth, the father, Cuchulain, slays his son. Madness ensues.
Cuchulain's fight with the sea is based on a tale from the ancient Irish sagas, in which the hero loses touch with his wife, Emer. Emer urges her son to find his father and wreak revenge on him, but Cuchulain is so powerful that he slaughters him.