Amberground is locked in darkness. A man-made star casts only a dim light over the land. The pitch-black wilderness is infested with Gaichuu--colossal insects with metal exoskeletons. The Gaichuu make travel between the cities of Amberground extremely dangerous. But thankfully the Letter Bees, a brave corps of messengers, risk their lives in order to keep the hearts of Amberground connected.

After years of searching, Zazie is on the trail of the Gaichuu that devoured his parents' hearts. But the hunt will force him to learn more about himself--and his past--than he ever imagined. And Emil, the kindly blind girl who runs the nearby inn, has an terrible secret...