The Nine Tailors (A Lord Peter Wimsey Mystery) by Dorothy Sayers

I have read this four or five times, and each time, I marvel at what Sayers accomplishes here—not only patterning a whole book around the obscure practice of change bell ringing (the "traditional English art of ringing a set of tower bells in an intricate series of changes, or mathematical permutations (different orderings in the ringing sequence), by pulling ropes attached to bell wheels"), but also writing a mystery of profound humanity. One of her four greats, alongside Murder Must Advertise, Gaudy Night, and Busman's Honeymoon.