Dark Inside, book 2: Rage WithinJeyn Roberts2013

In the first wave of the apocalypse that wiped out most of the world's population and turnes many of the rest into murderous Baggers, there are some survivors.
Aries finds it hard to be a leader when there are no easy answers and every move feels wrong. Clementine is desesperate to find her brother, Heath, but it's impossible to know where he'd be, even if he is still alive. Michael is haunted by the memories of his actions during his harrowing struggle to survive. And Mason is wrestling with something far worse: the fear that he may be a danger to his friends.
As the Baggers begin to create a new world order, Aries, Clementine, Michael, and Mason will have to trust and rely on one another more than ever in order to survive.