Whose Body? by Dorothy L. Sayers
I just finished my first Dorothy L. Sayers book, the first of her many mysteries starring an eccentric crime-solving aristocrat and his manservant-by-day, expert-photog-by-night valet. Imagine if Wooster and Jeeves went around solving mysteries, except Wooster was only pretending to be an ass, and there you have Lord Peter Wimsey and his butler, Bunter.
Quite apart from the quirky dialogue, puzzling plot and endearingly open-hearted discussions between Lord Peter and his policeman friend, this book is worth reading because the main character is a book hound. All through the novel he's sending his butler off to auctions to pick up rare editions for him, and Sayers thoughtfully includes footnotes for the reader which give details about the books requested, and whether Lord Peter was able to acquire them or not. As a book lover myself, I cannot express how satisfying I found this.
Pick this up if you've finished all the Miss Marple books and you're still hankering for a head-scratcher to eat up an afternoon.