After the battle of Tailtiu, the Tuatha Dé Danann choose Bodb Derg of Connacht as their new king. This offends Lir of the sídhe of Finnachad, and to placate him, Bodb Derg offers him one of his foster-daughters to wed. Lir chooses Aobh, who bears him two sets of twins: Aodh and Fionnghuala, then Fiachra and Conn. Sadly, Aobh dies in childbirth.
With Lir distraught, Bodb Derg offers him another daughter, Aoífe, to wed. Aoífe quickly grows jealous of the children and resolves to get rid of them. While journeying with them to the house of Bodb Derg, Aoífe demands that her servants kill them. When the servants refuse, she shoves the children into the water and transforms them into swans.
Though the children retain their human minds and speech, they will remain swans until Deoch, daughter the king of Munster, marries Lairgnén mac Cholmáin of Connacht. 900 years they will wander, 300 in Lough Derravaragh, 300 in the Sea of Moyle, and 300 on the west coast. When Aoífe finally arrives at the house of Bodb Derg, she is transformed into a demon as punishment.
The children bear Aoífe’s spell as best they can, filling the air with glorious music. Centuries pass and eventually they settle on Inis Gluaire in the west. One of Patrick’s followers, Mocháomhóg, brings Christianity to the island, and upon hearing the ringing of the holy man’s bell, the children begin to sing. Mocháomhóg is amazed and takes them into his home.
Meanwhile, Deoch and Lairgnén marry. The greedy bride hears of these magical swans and demands they be brought to her. Lairgnén attempts to fetch them, but at that moment the children regain their human form. They are old and frail. Mocháomhóg baptizes them just before they die.
Another version tells of the children regaining human form on hearing the toll of a church bell.