Under Wildwood by Colin Meloy (Book 2)
From Harper Collins:
Under Wildwood is the second book in the New York Times bestselling adventure series the Wildwood Chronicles from Colin Meloy, lead singer of the Decemberists, and Carson Ellis, the acclaimed illustrator of The Mysterious Benedict Society.
Ever since Prue McKeel returned home from the Impassable Wilderness after rescuing her brother from the malevolent Dowager Governess, life has been pretty dull. School holds no interest for her, and her new science teacher keeps getting on her case about her dismal test scores and daydreaming in class. Her mind is constantly returning to the verdant groves and sky-tall trees of Wildwood, where her friend Curtis still remains as a bandit-in-training.