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 knows what he has to do to save Amberground: unite the five children born on the mysterious Day of the Flicker. And his latest delivery may lead him to a man who has vital information. But meanwhile Lag has to cope with his brash new partner, Chico, who insists that nothing will stand in her way to becoming Head Bee!