Day 21 (The 100) is a good sequel to the first book, The 100. The Colonists are faced with the realization that they are not alone, and not all Earthborn people are welcoming.
This being said, I keep wanting the action of the show to come into the book, and it just hasn't happened yet. I am a bit disappointed by this, but I knew that it was going to be different. I have found that there is slow character development in the book, but quick character development in the show. There is beautiful detail of what a post nuclear Earth would look like in the book, where the show lacks this detail. I do really enjoy the books even if I am missing the action I was used to by watching the show first. I will be starting Homecoming now!!