A girl-child was born to Siobha on the night of a full moon. Her proud father, Feidhlim cradled her gently in his arms and named her Deirdre. He took her to the druids and asked them to foretell his infant's future. The druids looked towards the stars and glanced sadly at the newborn. "What do you see?" Feidhlim asked the druids anxiously. They answered "This child will cause great trouble. She will grow up to be the most beautiful woman in Ulster but she will cause the death of many of our men."

When the Red Branch Knights heard the druid's prognosis, they were uneasy and wanted the child immediately killed. They journeyed to the King and urged him to take action. King Connor was reluctant to deny the child's life and came up with a plan. "Deirdre will be reared far away from here and when she comes of age, I will make her my bride." This was deemed a satisfactory solution all 'round and King Connor set about finding an appropriate guardian for the child. He sent her deep into the forest to stay with a wise old woman called Leabharcham, who would care for and teach her.

As foretold by the druids, Deirdre grew to be a beautiful, though lonely young woman. One night Leabharcham discovered she had been sleepwalking and watched over her for the remainder of the night. When she awoke in the morning, Deirdre told Leabharcham of a dark-haired warrior who had been in her dreams for a month. "He is tall and handsome with raven-black hair. His skin is snow-white and he is fearless in battle." Leabharcham recognised Naoise, one of the sons of Uisneach from this description and her brow furrowed with worry. "He is Naoise one of the sons of Uisneach but you must not mention your dream to a soul. You are to be married to King Connor very soon."

Deirdre begged Leabharcham to send for Naoise so that she might meet the man of her dreams. Leabharcham refused at first, but seeing how unhappy Deirdre was, she quickly relented. Deirdre and Naoise met and fell in love at once. "I cannot marry Connor now" Deirdre said, "we must flee Ulster straight away." They set off and travelled all over Ireland but no one would help them, fearing the wrath of King Connor. Finally, they set sail and settled on an island off the coast of Scotland.

They lived happily on the island for five years until one autumnal evening, a messenger arrived from the King. The messenger conveyed King Connor's forgiveness and asked Deirdre and Naoise to return home. Deirdre didn't trust the King and wanted to stay on the island but Naoise believed the news and began to prepare for the journey home. They set off shortly afterwards but Deirdre had a sense of foreboding and begged him to turn back. Naoise reasoned with her, promising that everything would be fine. When they arrived, they were sent to the fortress of the Red Branch Knights instead of directly to the castle and Deirdre was convinced they were walking into a trap.

No sooner had they entered the fortress than they were surrounded. Naoise and his brothers fought bravely but they were outnumbered. They were captured and brought before the King. "Who will kill these traitors for me?" asked the King. None of the Red Branch Knights would kill a fellow knight. Suddenly an unknown warrior from another kingdom stepped forward and cut the heads off Naoise and his brothers with a single sweep of his sword. So great was Deirdre's sorrow that her heart broke and she fell upon Naoise's body joining him in death. Deirdre's father left Ulster for Connaught and joined Queen Maeve in many bloody battles against the Red Branch Knights. Deirdre had brought sorrow and trouble to Ulster just as the druids foretold.