The Midnight Library makes use of a speculative element in order to drive its central plot. Early in the book, caught between life and death, Nora enters the Midnight Library and is given the ability to see how her alternative lives might have worked out. This fantastical plot construct allows Haig to show scenes from these other lives in a way that feels tangibly real. This speculative quality in the story ends up elucidating many of Nora's greatest existential concerns. In making this interesting plot choice, Haig draws on a tradition of writing about parallel lives and alternative timelines.
In one of his most famous short stories, Argentine author Jorge Luis Borges constructs a story around the idea of infinite timelines. In the story "The Garden of Forking Paths," a spy named Yu Tsun tries to elude a British agent named Richard Madden. Set during World War I, the story details Tsun's work for the German empire while also recounting his interest in a manuscript written by his ancestor. This unfinished text was written in an attempt to capture every possible permutation of plotline, so with each decision a character made, separate chapters were written. However, because of the number of possible decisions, the novel became essentially impossible to write, as the number of chapters approached infinity.
In the story "The Library of Babel," Borges explores a similar concept. The story has no real plot, but instead simply describes a library that contains every possible combination of letters on a page. Due to the fact that many of the books are unintelligible, with some being written in languages that have yet to come into existance, the library is essentially rendered useless by virtue of its comprehensiveness. Its librarians drive themselves mad attempting to organize the books in a manner that makes them usable.
While Haig writes in a more humanistic way than Borges—whose stories read more like parables or philosophical quandaries—the central concept of the book is actually quite similar. Haig uses the existence of Nora's parallel lives as a way of highlighting the many possibilities that populate her seemingly hopeless life. Employing this speculative idea gives him the opportunity to make these possibilities more concrete to the reader.
