The Nightshade Chronicles #2: The White Assassin by Hilary Wagner

My name is Juniper, and I am keeping a life-changing secret from the other rats in Nightshade City. We've  imprisoned Billycan, but many of my friends don't understand why I haven't had the murderous rat executed. I'm hoping the serum we've given him will reveal a kinder rat than the most vicious killer we've known. I fear what might happen if Julius ever discovers Billycan is his real father. However, there is a more serious problem threatening our city. There's a traitor among the council. That's the only explanation for how Billycan obtained maps of our secret tunnels as he prepared for an invasion. The serum seems to be having a positive effect on him, but will it force him to reveal the identity of his accomplice? Are the changes just another sign of his trickery? How can I doubt the trust of my friends, when I'm keeping terrible secrets of my own?

I recommend you read the first book in the series to fully understand Billycan's evilness. This book had more mystery in it due to the unknown traitor. All of the characters are suspect, but several of them will be central in readers' minds. Clues are presented to change the attention, but my first instincts were correct. The author includes flashbacks to Billycan's time in the lab, and they help to explain his disturbing behavior. A couple of other lab rats return to become key characters in the current events. Juniper is the main character in this plot, as he tries to coax the truth from Billycan and battles with his own internal struggles. Again, I suspected his big secret, but I'm not sure it was as devastating as he made it seem. This book is more similar to Mrs. Frisby and the Rats of NIMH than book one, as the lab experiments were key factors in the conflict. As in that book, it's revealed that mice were also test subjects and have unusual intelligence and life expectancy, just like the test rats. Overall, I'm enjoying the series and recommend you give it a shot.