In her introduction to the 1995 Oxford World Classic's edition of the text, Alison Milbank stated that the novel's plot "unites action of a specifically Scottish medieval nature with the characterization and morality of the eighteenth-century cult of sensibility.

Whilst Athlin – "an edifice built on the summit of a rock whose base was in the sea"[1] – is home to a refined society headed by the gentle Countess Matilda and her children, Dunbayne is the domain of the villainous Baron Malcolm.

The novel's plot follows the young Earl of Athlin, Osbert, who seeks to take revenge against the unlawful murder of his father by the Baron Malcolm twelve years earlier after meeting the peasant Alleyn (who is later revealed to be the true heir to the castle of Dunbayne).

Osbert, whom "nature had given him a mind ardent and susceptible, to which education had added refinement and expansion," learning of his father's death wishes to lead his clansmen against Dunbayne to avenge him but is forbidden by his mother.

Alleyn offers to act as Osbert's guide through the countryside, informing the young Earl of Malcolm's poor stewardship of the surrounding lands and the people's displeasure with the Baron.

The imprisoned Osbert becomes aware that there are two ladies who appear to also be prisoners of Malcolm within the castle, and is comforted by both the idea of their presence and the beautiful music he hears from his cell.

Whilst the inhabitants of Athlin attempt to lead a rescue mission for their young Earl and Mary begs to be allowed to sacrifice herself for her brothers safe return, Osbert is able to temporarily escape his cell and discover the ladies of the Castle.