Act 1

It is 1921, and Séimí Gallagher has returned home to his childhood sweetheart 'Babaí Mháirtín' Friel. We are then taken back to 1873, days after Babaí was born. Séimí, aged five, visits the Friel household to see the new arrival (You Never Know...). As Séimí and Babaí grow up together, spending many happy days by the shore (I’ll Tell You A Story), they dream of sailing away to the golden clouds on the horizon, believing them to be castles where the fairies live (Castles Of Gold). In his late teens, Séimí befriends Cearrbhach, a gambling waster, who has just returned from working in Scotland. Cearrbhach takes notice of Babaí, who has grown into an attractive and sought after young woman. One Fair Day (It's Always An Occasion), Pádraig Ó Dálaigh, the local shopkeeper, makes an unwelcome advance at Babaí. The schoolmaster is also interested in Babaí. He is encouraged by Babaí’s mother, who thinks that a master's salary would give her a great start in life. Because of her apparent popularity, Babaí is mocked by her friends (Who Will She Marry?). Evictions are a regular occurrence (The Eviction), and Cearrbhach's elderly mother dies while they are being evicted from their home (Betty's Death). Afterwards, Cearrbhach 'goes on the run', following the death of a soldier during a confrontation that takes place at his mother's funeral while the outspoken local priest Father O'Donnell is being arrested (The Arrest / The Officer's Death). Séimí and Babaí reminisce (Castles Of Gold - Reprise), and effectively become engaged (Won't You Be With Me?), but Séimí, like most other young men of the time, has to leave to find work in Scotland. He hopes to earn the fare to America, from where he will send for Babaí. They plan that when their fortune is made, they will return home.

Act 2

Séimí sails to Scotland, unsure of his future (Course Of Time), and finds times hard there. He feels uncomfortable socialising (Séimí’s Highland), always thinking of Babaí (Thoughts Of Babaí) waiting for him at home. Séimí and Michael Dubh, another worker from home who freely offers his worldly advice (The Ballad Of Nuala Bán), both leave Scotland for America. Many years pass during which Séimí and Babaí wonder if they will ever be re-united (Sometimes I Wonder). While Séimí celebrates finding gold in the Yukon (Welcome To The Yukon) he remembers Babaí and their happiness back home in Cloghan Dubh. His thoughts are so vivid that he, even for a moment, thinks he sees her. He continues to prosper in Canada. Cearrbhach risks returning home because of his need to tell Babaí of his feelings for her. Babaí's "friends" still mock her (If Only She Had Married), knowing that she is still waiting for Séimí. It is now 1921, and Pádraig Ó Dálaigh, still bearing a grudge, tips off the Black and Tans that Cearrbhach and others are using Babaí Friel's house as a 'safe' house (After Pollen Barracks). The Black and Tans proceed to burn the house, and Cearrbhach is shot dead as he saves Babaí's life (Cearrbhach's Death). A short time later, Séimí returns home. He visits Babaí and learns of the many changes that have taken place while he has been away. He realises that almost everybody he left behind has moved away or died, and that he cannot stay. He leaves Babaí, who can't take in what has happened (Just Good Friends). Their true destiny ends the story of Caisleáin Óir.