The plot is a fictionalised account of the parents of Erasmus — Gerard and Margaret — and the many obstacles that stand in the way of their relationship.
The book made an impression on me when I read it as a child. The authority figures in it are presented as largely hostile and unreliable. The comprehensive cynicism about social authority, and about its supposed benevolence, distinguishes the book from other nineteenth century novels.
It is even more in contrast with current literature.
In modern fiction, even if some part of the establishment is behaving badly, there is almost always some part of it whose behaviour accords with the ideal, in which many people would no doubt like to believe.