Wildwood Dancing by Juliet Marillier, fantasy/myth category
Jena and her 4 sisters have a secret. Every full moon, they find a portal into the Other World and dance the night away. But things are changing. Their father must leave their home and spend the winter away for his health. He leaves the castle in the care of Jena and her older sister Tati, and reminds them to ask their uncle for any help they need. But after he leaves, their uncle is killed in a hunting accident and their cousin Cezar takes over. And wow, does he take over. Suddenly the girls have little control over anything, because Cezar knows best.
Add to this the twist that Tati falls in love with one of the other visitors to the Other World, one who hangs around with a suspicious crowd. Vampires, anyone? Jena's own companion, a frog, starts acting differently too. It seems like just when things can't get any worse for the family, they do.
I really enjoyed this book. It's a mix of vampire folklore (it's set in Romania), the 12 Dancing Princesses and The Frog Prince, but it works surprisingly well. I really liked Jena, despite her flaws, and I loved the ending. Then I found out there's a sequel, Cybele's Secret, which might not be out yet. This one was a lot of fun.