What does it mean to be human? That is the question Rick Yancey poses in this novel. It is a story about an alien invasion, about beings who are determined to wipe out all of humanity. They hide in our bodies turning the true humans against each other. Scary science fiction aside, this novel is about so much more. It delves into the human psyche. What do we sacrifice to be truly human? Is it in our DNA to sacrifice self for the life of another whether or not we care for that person? Time and again we’ve seen it in the headlines, how someone dove into a raging river to save someone, or rushed into a burning building to save an unknown person. Why do we do it? What causes us to self-sacrifice? Is it the ability to sacrifice our selves for another that makes us truly human? Is that the litmus test?