Hidden beneath the ruins of Astraca, the legendary city destroyed by raging fires more than a century ago, hides the last sanctuary of the Mayake people—if only they can reach it. Hounded relentlessly by the Gaijins, the Mayakes are in a race against time as they search desperately for the entrance to Astraca’s fabled Underground City. Young Athel and his friends know the only way to enter the City is to solve the mystery of the engrams, bits of encoded memories passed from one generation to the next. What they don't know is that even if they elude the Gaijins' latest threats and succeed to escape, the Underground City has its own secrets to reveal. Secrets that could either save the Mayake people or make the Gaijins' work a lot easier.