Cinder by Marissa Meyer

Cinder by Marissa Meyer -- 390 pages

There's a prince, there's a ball, two steps sisters and a step mom, but all resemblance to the fairy-tale "Cinderella" stops there. Cinder is a cyborg, and a gifted mechanic because of it. But her world changes when Prince Kai himself steps into her booth to bring an android for her to fix. It seems very important to him, even though the android is out of date, an old model. Even though she used to laugh at girls who tripped over Prince Kai, she finds herself liking him, all the while desperate to make sure he doesn't find out what she is. 
But more than that will happen to Cinder. The plague is killing thousands of people, and via a cyborg draft, cyborgs are being tested in order to find an antibody. None of them have survived. 

I was thrilled and delightfully surprised by all the details in the plot. 

This is book one in the Lunar Chronicles.