Dexter works at a police station and solves murders. This is a good cover for him because then no one would suspect him but when he goes home at night he kills people. These people are bad and are the ones who slip through the cracks of the system. Dexter feels he is doing a good thing by killing them,
but no one can know or else he would be put in prison so he has to pretend he has feelings and cares about solving crimes. He can only be his true self when he leaves work and goes to his home alone.
Later on in the story Dexter is able to really learn how to love when he finds someone who is like him and loves him for who he is. Also when his sister dies he cries for the first time and realizes he needs to think about how his ways of life are affecting others. This is something he never thought he could do, which really says that sometimes we don't even really know ourselves. We think we do and we train ourselves to think we are one way but in reality there are some parts of us that are hidden away.
In conclusion "Character is what you are in the dark" is a quote that all of us can relate to and especially in the book "Dexter" it is not only a present theme but it is expanded upon in a way you wouldn't expect. We aren't always what we show to the world or even to ourselves. We all have qualities in us that not even we knew we had.