Changes by Jim Butcher

Long ago, Susan Rodriguez was Harry Dresden's lover-until she was attacked by his enemies, leaving her torn between her own humanity and the bloodlust of the vampiric Red Court. Susan then disappeared to South America, where she could fight both her savage gift and those who cursed her with it.
Now Arianna Ortega, Duchess of the Red Court, has discovered a secret Susan has long kept, and she plans to use it-against Harry. To prevail this time, he may have no choice but to embrace the raging fury of his own untapped dark power. Because Harry's not fighting to save the world...
He's fighting to save his child. From Goodreads

I said it last time I read one of the Harry Dresden books and I will say it again. I really like this series! There are two left, Ghost Story and then Cold Days that is being released the 29th of November on Kindle.
This one takes a whole new turn when Harry finds out he has an eight year old kid and the Red Vampires has taken her. He will do anything to save her. He again has to fight a lot of evil helped by friends, other people and beings only a little less evil than the enemy. All ends reasonably well or not.

This book qualifies for: 
100 books in a year Reading Challenge 2012, 
Goodreads 2012 Reading Challenge, 
2012 Ebook Challenge,
2012 Witches & Witchcraft Reading Challenge,
Finishing the Series Reading Challenge,
Thankfully Reading Weekend 2012