When Willa Cathcart Wilmerding, the bravest girl in the world, is told she must stop her nightly tradition of howling at the moon, she decides to run away. High in the mountains, she meets Buttercup the Bigfoot, a friend unlike any other! Willa and Buttercup do everything together. They leap up and down the mountains, soar over mighty crevasses, and make each other crowns of flowers - but their favourite thing to do is climb a high peak and HOWL at the moon.