Esmée Délancourt was perfectly happy never to leave her quiet home in Saint-Denis-lès-Chevreuse, France. But when the doors of the commuter train bound for Paris slide closed, trapping her inside, she finds herself an unwilling participant in an adventure through the City of Lights. As Esmée struggles to find her way home again, the little butterfly meets a cast of characters and witnesses a world of wonders she could never have imagined. Through danger, love, and loss, she comes to understand the meaning of the word home and the symbolism hidden in a sculpture tucked away in the Louvre Museum; a sculpture her mother used to teach an important childhood lesson.