Shift - the Silo Saga goes back to where it all started.

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.