Poison

Poison by Chris Wooding is a dark phaerie tale.

Poison, a stubborn girl who lives with her father, her step-mother and her half-sister Azalea in the Black Marsh, wakes one morning to discover that the Scarecrow has stolen her sister and replaced her with a changeling.

Though none who live in Gull travel, she finds a way to the nearest city, on the trail of anyone who can help her get her sister back. Along the way she collects a strange group of friends and helpers. But will they be able to save her sister from the phaeries? Will Poison and her friends survive the tests they have to pass to set Azalea and themselves free of the other realms?

Wooding, Chris. (2003). Poison. New York: Orchard Books.