Somewhere between the short story and the novel is the novella, a piece of prose long enough to require sectional divisions in the text but still short enough to read in one long sitting. Because the form gives enough space to describe a different world but doesn't require a writer to come up with a complex plot, there are a lot of post-apocalyptic novellas; individual flavors range from politics (Ayn Rand's "Anthem") to horror ("The Mist" by Stephen King).
"Genesis," by Bernard Beckett, is almost a prototypical sci-fi novella. In the book, human civilization as we know it has been devestated by a plague, and a handful of survivors have formed a society on an isolated island. Rather than thrusting the reader into the middle of this decaying world, though, Beckett opts for a far-future Republic centuries removed from the original plague. Here, a youth named Anax tries to enter an elite Academy by taking a grueling Socratic entrance exam that tests her knowledge of historical hero Adam Forde. It's a good premise, and a tidy way of dumping a lot of exposition on the reader without the narrative collapsing.
That doesn't mean it's great literature, though. As Anax describes the life and times of Adam Forde, it's hard not to raise a few eyebrows at the massive plot details being glossed over in her dialogue with the Examiners. The final revelatory twists are clumsy, more M. Night Shymalan than Rod Serling. Still, as a way to jump-start an epistemological discussion in a ToK class, it's a decent first-day read.