Basically it's a zombie survival story and a typical one, if you've watched any of the Walking Dead or any zombie film ever, you have an idea of what to expect. Zombies are dangerous and humans more so.
The characters are actually really good, with neither Mallory and Mckayla being fluttery young women, they are both strong, capable and hardened survivors. There is no stupidity in their reasoning and both read as true survivors in a world gone to hell. The lack of angsty moralising is refreshing and I actually like the pragmatic approach from both sisters.
The writing is occasionally problematic with some very laboured description at times but well written action sequences make up for it.
All in all, this is a good, fairly gripping read.