The Silo Saga enters its final book set up for success. Wool painted a picture of a bleak future where a dystopian underground society is all that manages to keep humanity on the right side of extinction. Shift then revealed who was behind the building of the silos and their published plan for delivering mankind to a better future; however, it also exposed that the official plan intentionally leaves out that a key decision will eventually made about who will and won't survive. All of this makes for excellent backdrop as the characters from both books converge to determine the ultimate fate of mankind.

Author Hugh Howey does a masterful job slowly revealing how his unique dystopian world functions during the first book of the series, Wool, but he never touches on the subject of how society morphed into that state. Well that is exactly what he does in Shift, as some much needed context is added to explain why things are the way they are. Since he jumps back in time to our contemporary world he needs to introduce a whole new set of characters, which is initially off-putting, but it eventually all comes together and sets things up for an excellent finale to the series.

With the Earth in a state of ruin, mankind has retreated to living underground where a dystopian society has evolved to ensure continued existence. The inhabitants of the underground silo know that their self contained ecosystem is a fragile balance so they must dole out harsh consequences to anyone who disobeys the rules. These people have lived underground for generations and know nothing of how they got there or why the outside world is so inhospitable; however, they do know that crimes are punished by being sent outside through the single airlock at the top of the silo. The world outside is so toxic that even their best protective suits offer only offer a couple of minutes of life, yet everyone sentenced to die this way is asked to perform a vital service for the rest of the silo before they perish - a cleaning of the external sensors. Would you do such a favor for those who sentenced you to die?