Act I: Lavarcham's house on Slieve Fuadh. Conchubor, the aging High King of Ulster, has charged Lavarcham to raise the child Deirdre to be his queen when she comes of age. Lavarcham finds that the now-beautiful Deirdre is a willful young woman, without interest in marrying an old man. Conchubor comes to Slieve Fuadh to bring Deirdre to his palace, Emain Macha, ignoring her pleas to remain in the countryside for another year. After he leaves, Naoise, son of Usna, and his brothers come to the cottage seeking Deirdre, and she tells them of her summons. Deirdre is aware of a prophecy that she will be the doom of the sons of Usna; nonetheless she asks Naoise to take her away from Ulster. He agrees, and Ainnle weds them in an impromptu ceremony.