This book is the ninth book in the series begun with Anne McCaffrey and Margaret Ball's "Acorna the Unicorn Girl" and the second in the continuation series, Acorna's Children, following on from the original books centred around Acorna. The original Acorna books are a must-read if you are to completely understand the setting for these books, as very little background information is given in this novel, and events and characters from the previous stories are referred to frequently. You will also need to read the first in this series, "First Warning".
In "Second Wave" the plague is no longer killing people but will start to attack in a new way. Khorii's parents, Acorna Harakamian-Li and Aari, along with their friends Captain Jonas Becker, RK (Roadkill) the cat and Maak the android are in quarantine, still infected with the plague organisms which only Khorii can see. She sets off with her cat Khiindi, and her android brother Elviiz to try to find out how the plague works, but all does not go to plan, with interruptions from new friends, space pirates, Marl Fidd, and the arrival of Khorii's twin sister, Ariinye or for short Ariin, who was stolen from Acorna's womb before they were born.
And it all has something to do with Khiindi, who is clearly not just an ordinary Makahomian Temple Cat...
I would say that the characterisation is just as shallow in this book as in the others, and overall the characters are a bit too nice although some interesting people appear in this book - I wish they had been developed in more detail.
The plot gets more exciting yet complicated. It can be hard to keep track of what Khorii and her friends are meant to be doing as opposed to what they actually end up doing instead for a while every journey they take. This is why I give this book three stars rather than the four "First Warning" received from me.
I would recommend "Second Wave" and the rest of this series for mid-teenagers most as the principal characters are around that age themselves. The ending of this book is left open for the story to be concluded in the third and last novel in the Acorna's Children series, "Third Watch".