The Investigation by Stanislav Lem
Cracking the code to this book was a little like riding a three-dimensional roller coaster traveling in slow motion. This police procedural asked the 'question' (as in inquisition) over and again, each time with a slightly different bent. This could get monotonous. Nevertheless, I found myself wanting to see what the next query would reel in. Very intelligently drawn characters operating in a miasmatic atmosphere.
Finally, although the last four paragraphs were straightforward, I found myself interpreting them abstrusely.