The Silo series is at it's heart a mystery. Wool works because it drags us into the murky workings of Silo 18. The kicker (*Wool spoilers ahead*) that the inhabitants of the Silos are the ones who killed the world is one of the better twists in science-fiction.

Shift, as a prequel to Wool, doesn't have the same emotional impact. The question is 'Why are the Silos?' rather than 'What are the Silos?' and the answer is neither as convincing nor compelling as the one in Wool. The story bounces between the origins of the Silo project in near future, an earlier revolt in Silo 18, and how Solo became the last survivor of Silo 17, trading cheap cliffhangers for real emotional investments.

Shift's not bad, but it's nowhere near as good as Wool.