In Amberground, a land lit only by an artificial sun, Letter Bees risk the dark wilds to carry mail between towns past the armored insects called Gaichuu. Lag Seeing reached his aunt's house as cargo himself, delivered by the Letter Bee Gauche Suede after his mother was taken from him. Years later he sets out for the capital to sit the Bee entrance exam, hoping to find the man he idolizes. Along the way he meets Niche, a strange girl who becomes his dingo, the companion every Bee travels with.