One of my very favourite detective fiction tropes is the Unidentified Corpse.  It’s at the heart of my favourite E.C.R. Lorac book, one of my favourite Freeman Wills Crofts books, and as a mainstay of the work of R. Austin Freeman is put to wonderful use both traditional and inverted. Murder in the Basement (1932) by Anthony Berkeley also invents the Whowasdunin?, giving us a cast of characters from which the corpse will be produced, and not divulging the identity of the victim until the halfway point. Thankfully, given Berkeley’s tendency to commit to a thought experiment regardless of whether the book that comes out of it is any good, he’s also written an entertaining and very witty novel along the way.