This is one of the three great love stories in the Irish Myth tradition.  King Conor MacNessa had taken the kingship from his foster father, Fergus Mac Rioch for a year but had shown such wisdom that it was decided he should stay on as king.  Shortly after this decision, Conor and his Red Branch Warriors were at a feast in the house of Felimid the Harper.  Felimid was in high spirits because his wife was about to give birth.

He asked Conor’s druid, Cathbad, to make a prophecy as to what was in store for the baby.  He told them she would be the most beautiful woman who ever lived but she will cause trouble by splitting the Red Branch in two.  At this the Red Branch demanded that the baby be killed.  But Conor wished to preserve his reputation as a wise king said he would take care of her, in secret, and if she was so beautiful, he would marry her to avoid trouble.

Deirdre was then brought up in a hidden valley by an old nurse, Leabharcham, who was very protective of her.  From time to time, Conor would visit but Deirdre did not have much affection for him.   Who she did have love for is a man with hair as black as a raven, skin as white a snow, and cheeks as red as blood.

Deirdre asked Leabharcham did she know anyone fitting this description.  She told her about Naoise, a warrior of the Red Branch.  She pestered her to let her see him.  Initially Leabharcham refused, but eventually relented.  She told the three Sons of Uisneach of the wonderful hunting in the valley and indeed they came to hunt.  Deirdre immediately fell in love with Naoise, and so did he with her.  She asked him to run away with her.  He refused because she belonged to Conor.  But she put a geasa on him, so he had to run away with her.