A young man working in a rural Irish library becomes entangled in the philosophical and existential musings of a mysterious American visitor. The narrative follows the protagonist, an unnamed librarian, as he encounters James Knowth, a man obsessed with the writings of the fictional philosopher Jean-Marie Lart D'Aurevilly and the concept of the 'archive'. The library itself, a repository of forgotten texts and obscure knowledge, becomes a central metaphor for the characters' search for meaning and truth amidst a world that often seems absurd and nonsensical. The story unfolds through a series of dialogues, philosophical discussions, and surreal events, challenging conventional notions of reality and authorship.

The Dalkey Archive is widely recognized as a complex and challenging work of metafiction and philosophical satire. Critics often highlight its intricate structure and its engagement with existential and epistemological questions, noting O'Brien's distinctive blend of humor and intellectual depth. The novel's exploration of the nature of reality, authorship, and the role of the archive has cemented its status as a significant contribution to modernist and postmodernist literature. Readers often find it a rewarding, albeit demanding, experience that prompts deep reflection on the construction of narratives and the search for truth.