If you're curious about the Dorothy L. Sayers' essay "Gaudy Night" referred by Julian Symons in Bloody Murder, it's published in the essay collection The Art of the Mystery Story edited by Howard Haycraft.
If you're curious about the Dorothy L. Sayers' essay "Gaudy Night" referred by Julian Symons in Bloody Murder, it's published in the essay collection The Art of the Mystery Story edited by Howard Haycraft.