I'll confess to a deep fondness for The Caves of Steel, a sociological novel wrapped in a light mystery. In the far future, an over-populated Earth is dominated by giant hive Cities, and the galaxy dominated by the 50 Spacer planets. When a prominent Spacer is killed on Earth, Detective Elijah Bailey is assigned the case, and an unusual partner in the form of a nearly perfect humanoid robot, R. Daneel Olivaw.

The mystery is really an excuse to explore the world of the Cities, where humans lived crammed together in vast communal blocks linked by moving pedestrian expressways, subsisting on food made mostly from varieties of yeast. Hidden political cadres of medievalists seek a romantic return to the soil, even though modern humans are psychologically incapable of living under an open sky. Meanwhile, Spacer renegades have their own plan to use Terrans to launch a new wave of colonization.

The extrapolation of a setting is some of Asimov's best work, and the mystery good enough to keep you reading.