Shift is the second book in Hugh Howey's Silo trilogy and as a prequel to Wool it doesn't quite stand alone as an idenpendent book - more like a bridge between the first and the last book of the series explaining how everything came to be. If you haven't read Wool yet but are planning to (which I warmly recommend you do even if you wouldn't otherwise be the biggest sci-fi fan) don't read any further because there might be some spoilers.
In modern Hollywood films I often find it a bit disturbing that nothing is left for imagination any more. Instead you are shown every gruesome act of violence and graphic sex scene, even though what we don't see can often be scarier or sexier than what is right there in front of your eyes. Think Hitchcock's Rearwindow and the suspense they were able to build without actually showing anything. It's like we can't think for ourselves anymore and need instant answers to all our questions.
As a prequel the main purpose of this book was to tell the readers how we ended up in a situation where the environment outside has become uninhabitable and people are confined to living in under-earth silos. However I found the given explanation a little far-fetched, lame and unconvincing and the alternative, as in not knowing why, much more intriguing. I kind of liked being oblivious to the history and the dangers of the outside world the way the people living in the silos were, and wondering whether the distruction was down to a war, climate warming, pollution, a nuclear accident or one the other sinister threats we fear for our future.
I think I can safely assume that you can handle some Star Wars comparisons without finding me too geeky - after all you are reading my sci-fi book review. Not knowing what was going on outside the silos was like the force in the Star Wars saga. The jedis had it and I didn't think any further explanation was needed like a magician's trick looses it's point if you know how it was done. Then they make the prequels and in Episode I (Phantom menace or whatever it's called, the one with young Anakin Skywalker and that annoying Jar-Jar Binks) Qui-Gon Jinn takes a blood sample from Anakin for an analysis and says it's rich with midi-chlorians which apparently is synonymous with being strong with the force. After that I kind of lost the interest - way to spoil the mystery and totally unnecessary for the story line. I felt the same way about the nano-machines in the air causing the people dying if they ventured outside the silos in this book series. Or if you come up with something like that at least explain it a bit better than just leaving it all very vague.
The book introduces a whole new cast of characters and only in the last few pages do we reach the events of the first book, Wool. The story is told mostly from the point of view of the Silo 1 as well as giving us insight of what went down in Silo 17 where Juliette met Solo in the previous book. The story wasn't quite as good as the first of the series but still good enough for me to want to read the last one and see how everything will end.