For me Gaudy Night is one of the most successful marriages of the puzzle with the novel of social realism and serious purpose. It tells me, as a writer of today, that it is possible to construct a credible and enthralling mystery and marry it successfully to a theme of psychological subtlety, and this is perhaps the most important of Dorothy L. Sayers's legacies to writers and readers.
From P.D. James, Talking About Detective Fiction (2009).