Several years ago, a virus began wiping out whole populations. The last surviving adults know their days are numbered. Strangely, children born after the start of the virus are all hybrids: part human, part animal, and not susceptible to whatever the virus is. The hybrid kids don't get sick. Gus is 9 years old and has lived in isolation with his father all his life. His mother died when he was too little to remember, and his father is dying now. He warns Gus about leaving their camp, but after his death, Gus has no choice: hunters have found him, and it's only with the help of a mysterious, dangerous stranger that Gus survived. Jeppard promises to take Gus to the preserve, where hybrid children are safe, and Gus really has no choice but to believe him. 
 Post-apocalyptic in that the world has crumbled and the population is significantly reduced; the world is now a violent, lawless place in which hybrid children have bounties on their heads. For a kid with no experience of the outside world, every interaction is laced with hope and fear, promises of salvation and destruction. 
 Could be 8th grade and up; the violence is not graphic but still very present, making me err more on the side of high school. Readalikes: The Road (McCarthy) for the travel to an assumed safe haven; Z for Zachariah (O'Brien) for the need to trust a stranger for survival; The Roar (Clayton) or X-Men (Marvel Comics) for mutations. 
 Waiting for the next 2 books to come into the library to make any real judgements about where this is going; I liked this well enough but it's really too short to get a good idea of the characters and overall plot.