The premise is that a young man named Baron is coming to one of the many pocket communities that remain in the apocalypse. It's not armies of free-range zombies wandering around the world but random outbreaks of infection that cause things to go to hell. Baron is a loner, like Mad Max, and doesn't want to stay too long in town because things tend to go bad when he sticks around too long. This is almost immediately proven when an outbreak happens and he ends up killing some people in self-defense after fighting off a zombie.
Unfortunately, one of those people he killed was the slave bodyguard (called a "Gin") of a woman named Talia. Talia is of a new breed of humanity that is immortal and while she's the youngest member of their race, harming her property really ticks her off. It doesn't help that the man Baron killed, Mickey, was beloved by the other survivors and the only thing keeping them from tearing him apart are the dual issues of the outbreak as well as the fact Talia needs a new Gin to replace her old one. So Baron ends up collared and forced into service of a woman who hates him.
Oddly, it's less of an unequal pairing than you might think because Talia doesn't know how to survive outside in the Wasteland nearly as much as Baron. They're also both teenagers, or at least look and act like them [due to age being nebulous in this strange world], so they aren't used to exploiting power structures. Baron is, of course, attracted to Talia while she also develops feelings for the young man that is seemingly primal. The Mad Max paralells are pretty depe given that Baron has been alone for so long he barely remembers how to interact with his fellow humans but doesn't carry any of the malice other people do. He just wants to survive and be free (as well as get himself a mate).
The world Megan Mackie has created is unlike most zombie apocalypses because the virus that created them doesn't kill you but makes you immortal. People have actually recovered from being a zombie in this world and returned to sanity. Which, unfortunately, probably means they got bit again and became them again. This means that killing the undead isn't a chief priority for many. It raises questions on whether zombies have to eat or do other activities while undead but is an interesting twist on the subject. We also have the immortals living in the ARK that consider themselves gods compared to regular humanity and Baron simply does not understand.
Overall, I think this is a pretty fantastic YA dystopian zombie novel and people who like that sort of thing will like exploring its surreal world. There's some dark things in the book like poor Talia's past history of being experimented on that might set people off but not that much worse than anything in THREE OF CROWS or THE HUNGER GAMES. I think people should really check this out.