Thus ends the Magic Or Madness trilogy by Justine Larbalestier. The concept of magic in this book is one of the most interesting I've come across. I reviewed the second book, Magic Lessons, here. In Reason Cansino's world, being magical leaves a person with two options - an early death or insanity. Magic used only a little at a time can result in a bit longer lifespan, but the only way to truly live long is to take magic from someone else.
Reason, her friends Jay-Tee and Tom, and Reason's grandmother are trying to destroy Reason's grandfather who in turn wants to steal their magic from them. Reason is pregnant by Jay-Tee's brother Danny and the child is imbued with "Cansino Magic" which is even more potent than regular magic because in the second book Reason's ancient grandfather changes Reason's DNA which is gradually making her less human and more of a magic being.
I liked the third book well enough, good closure, good drama, a fun sort of unexpected romance thrown in for good measure.