The Moon Key.

Small and silver, Wendy's only memento of her parents is a crescent-shaped pendant that opens the door to a new world - a magical world. Soon Wendy will be swimming with the sea lions at the Central Park Zoo and lighting the torch on the Statue of Liberty, all due to her newfound magical talents. But Wendy's powers come with a cost. She's being tested for some reason, and she doesn't know why. Are her parents involved? Will her foster brothers survive? Wendy wants to be a heroine, but first she must learn the true meaning of courage - and the sacrifices we make to protect the people we love.