Horatio M———, the younger son of the Earl of M———, is banished to his father's estate on the northwest coast of Connacht (i.e. County Sligo) as punishment for accumulating large debts, neglecting his legal studies, and "presiding as the high priest of libertinism at the nocturnal orgies of vitiated dissipation"[1] during his life in London.

Living in the castle are the Prince of Inismore, his daughter, the beautiful and talented Glorvina, and their devoted Catholic priest, Father John.

Through conversations with the family, Horatio learns a new respect for Irish history and culture, which Owenson underscores in extensive footnotes, made in the seemingly objective voice of an editor; these footnotes both expand on and defend the Irish cultural and historical arguments made by the Prince and Glorvina.

Their courtship gets halted by Horatio's father's plan to marry his son to a wealthy heiress, and by the existence of a mysterious suitor for Glorvina's hand.

A seemingly omniscient third-person narrator takes charge of the denouement, explaining how Horatio gets saved from having to make this mercenary marriage when his intended runs off.