The novel is about the complex friendship and relationship between two teenagers, Connell and Marianne, who both attend the same secondary school in County Sligo and, later, Trinity College Dublin (TCD).
It is set during the post-2008 Irish economic downturn. Connell is a popular, handsome and highly intelligent secondary school student who begins a relationship with unpopular, intimidating yet equally intelligent Marianne, whose mother employs his mother as a cleaner.
Connell keeps the affair a secret from school friends out of shame but ends up attending Trinity with her after the summer and reconciling. Well-off Marianne blossoms at university, becoming pretty and popular, while Connell struggles for the first time in his life to fit in properly.
The pair weave in and out of each other's lives across their university years, developing an intense bond that brings to light the traumas and insecurities that make them both who they are.