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.

Lag, now a Letter Bee rookie, meets Dr. Thunderland, Jr., a peculiar man who collects and catalogs the various Amberground species. When the doctor takes a particular interest in Steak, Lag and Niche have to hustle to keep him off the doctor's dissection table! The ensuing chaos pays off for Lag when the doctor reveals that Gauche--Lag's missing hero--paid the doctor a visit before he disappeared.