The short version: great book. Very readable. Go buy.
Magic or Madness is one of the best YA books I've read this year, and I've already read a stack of them. It begins in Australia, with a girl named Reason who's just, after years of fleeing, ended up in the custody of her grandmother, whom her mother always told her was an evil witch. Except now her mother has attempted suicide and been placed in an institution, and Reason is planning how to escape.
Reason doesn't believe in magic.
There's also a boy named Tom, who loves fashion design, has a crush on Reason, and is her grandmother's protege.
And in New York, a girl called J.T., whose magic power is being sucked from her by a vampiric sugar daddy.
The book isn't that long, but Larbalestier worked in a lot of conflicts between truth and lies, and science and magic, and sacrifice and magic. Her magic has costs, big ones, and the choice Reason must make at the end is only partially a happy one. My only complaint is that the ending felt a little rushed. Only a little. The denouement helped mitigate that, and it doesn't affect my recommendation at all.
Go read this book.