Amy is one of the last living humans from Lepingville (same town Jessie is from in Dust) and she's decided it's time to move on. Traveling through the wasteland of neighboring towns on her way anywhere, she meets Lisa, an ex -- Lisa was human before the outbreak that turned everyone, human and zombie, into something other. Everyone but a handful of frails, those like Amy who were unaffected by the infection. Then Lisa and Amy are taken to a small town where exes are masters and frails have become all but slaves. The order of the world has been permanently swayed and Amy will have to cope if she is to survive. At least with an ex on her side, things are looking up a bit. But Amy is trailed by her own guilt and a creature that could be her imagination or something worse.
Frail takes place after DUST in the trilogy, but features a human protagonist.
It's hard to tell at this point just where the trilogy is headed. Like Jessie in DUST, Amy is kind of losing her mind and the narrative reflects this. There are some return characters from Dust as well. Lisa, of course, but some of Jessie's old gang, too. And it's unclear just why Lisa is keeping secrets from Jessie's old pals.
As zombie reads (and reads in general) go, this series is original and well thought out. There are some really great aspects in terms of the zombie lore and the experiments that caused the outbreak in the first place. The conflict between zombies and humans and then ex humans and ex zombies is interesting, obviously paralleling common us vs them themes. It'll be interesting to see who will return in book three and where the story will end.