The summary of this one-act play makes a lot more sense when the reader realizes that Cathleen ni Houlihan is actually the personification of the movement for Irish independence. She exists to convince the young, Irish men to fight.
They shall be remembered forever, They shall be alive forever, They shall be speaking forever, The people shall hear them forever.
In short, the story is about the Gillane family and their hopes to get out of poverty. Peter and Bridget Gillane have two sons: Michael and Patrick. Michael is engaged to be married to Delia Cahel, and the family couldn't be happier. Why? Because Delia brings a dowry that will help the Gillane's work the land.
Here is where Cathleen ni Houlihan shows up. Cathleen ni Houlihan first appears as an elderly woman, quite careworn. She knocks on the Gillane's door hoping to enlist the young men of the household to fight for her four stolen fields. Cathleen ni Houlihan admits that it will take both sacrifice and blood.
Michael gives up his happy future as a husband to follow Cathleen ni Houlihan and to sacrifice himself for Irish independence. As soon as Michael vows his life, Cathleen ni Houlihan appears now as a strong, young woman and, in fact, a queen.