The Bunker Diary book by Kevin Brooks

I can't believe I fell for it.
It was still dark when I woke up this morning.
As soon as my eyes opened I knew where I was.
A low-ceilinged rectangular building made entirely of whitewashed concrete.
There are six little rooms along the main corridor.
There are no windows. No doors. The elevator is the only way in or out.
What's he going to do to me?
What am I going to do?

People are really quite simple, and they have simple needs. Food, water, light, space, privacy. Maybe a small measure of dignity. A bit of freedom. What happens when someone simply takes all that away?