This is the story of a community living in a closed-in world called the silo. We soon learn that all is not well; people who question the system are sent outside to clean the sensors/cameras which show a view of the outside world on a big screen in the top level, the cafeteria, which is buried just below ground level. Anyone who goes outside isn't expected to return - and doesn't. 
 The story is told in a number of sections, which I've since discovered were published individually as novellas, though confusingly Goodreads has put the omnibus edition on the same 'page' as the original first novella, so I had to move my review to the omnibus. Each focuses on particular characters and as the story goes along, tension builds as more is revealed. The characterisation is very good, particularly of various elderly characters who are created as real individuals, and there is quite a lot of tragedy along the way as well as some edge of the seat suspense in the final couple of sections. 
 It is also interesting that one of the heroes of this story - Juliette - is an engineer. That's a nice twist. In fact, the story celebrates the ingenuity and resourcefulness of Mechanics, as they are known, over the dishonest and ultimately murderous actions of the IT personnel. I did find the characterisation of IT people in general somewhat unbelievable having personal experience of the industry, and it is also rather a puzzle as to what all these IT people actually do (apart from the few who conduct the spoiler-based activities which the reader eventually learns about), especially given that so many facets of society which would normally be computer controlled or aleviated are deliberately done the hard, low tech way. 
 Another thing I had an issue over was the underlying premise. It just was not terribly convincing. (view spoiler)[It seems the US government didn't like the way the world was going so they built enormous silos - 50 of them in the story's big 'reveal' - and filled them with the sort of people who would form a 'homogonous' community. The story comes across as if there is no one of an ethnic background whatsoever unless I've missed something. These corrupt authorities then - even bigger shock - brought about the catastophe which made life outside impossible for anything whatsoever, even insects - and given that cockroaches are expected to be able to survive atomic radiation, that seems a bit unlikely. In any case, it is far too extreme - if a government was that wicked, they could surely have 'done the job' by releasing a plague, having already made the chosen people immune. That would have given them a depopulated world which still had the plant and animal ecosystem available for their use. I also found it hard to believe that the supplies of oil and mined resources beneath the silo would not have run out after centuries, especially when it turns out there isn't just one silo! 
 The governmental project doesn't work anyway - there are huge social injustices and inequalities built into the job-based caste system so there are bound to be uprisings etc from time to time - which even the 'wool over the eyes' general populace is aware of though only whispers about to avoid being sent for 'cleaning'. So the original goal of having a community where everyone is interdependent and there are no tensions, as evil Bernard tells Lukas, is defeated from the start! I also found it lacking in credibilty that Bernard plans to send loads of rebels cleaning, in the deliberately sabotagued suits, including those who surrendered and were probably non combatants, when this would rob the silo of anyone with engineering experience, and it has been made clear all along that engineers (called 'mechanics') are vital to the continued survival of the community. Perhaps he is meant to be a irrational megalomaniac - he shows signs of that from time to time - but even his kowtowing security chief would surely point out that they need engineers to keep the lights on, the water pumped out of the basement and the air circulated! (hide spoiler)] 
 So 4-stars for excellent characterisation, good action, an interesting idea but the lack of credibility if you really think about the premise means I can't award this 5 stars.