The Name of the Rose by Umberto Eco (1980)

Seven deaths in seven days, each one answering a trumpet of the Apocalypse, fall upon a snowbound Benedictine abbey, and a Franciscan friar called William of Baskerville arrives to read the bodies the way he reads everything else, drawing a whole story from a smear of ink on a dead man's finger or the print of a horse in fresh snow. Umberto Eco gives this monastery a library that is a sealed labyrinth, a place where knowledge has been built into a maze precisely so that no one may wander it freely, and somewhere inside waits a single book so dangerous that men kill to keep it shut. What the book argues is that laughter is no sin but a kind of truth, and the fear of that idea is the real murderer here. Eco builds the most ingenious mystery imaginable and then lets its detective reason brilliantly, and not quite rightly, toward an answer that solves less than it mourns. You finish it convinced that a library is the most thrilling and most terrifying room ever made.