The Cruel Prince by Holly Black
One terrible morning, Jude and her sisters see their parents murdered in front of them. The fearsome assassin abducts all three girls and brings them to the world of Faerie, where Jude is installed into the royal court. Mocked and tormented for being merely mortal, Jude soon realises that to survive in this treacherous, dangerous, new world, she needs to be a smart, cunning and deceitful as the Fey themselves.
This is the first book in the series 'The Folk of the Air'.
The second book 'The Wicked King' is also available.
