Bartlett and the City of Flames

In Bartlett and the City of Flames by Odo Hirsch, the sequel to Bartlett and the Ice Voyage, the explorers Bartlett, Jacques le Grand and young Gozo are captured by guards from the City of Sun, and the powerful Pasha thinks Gozo is his long-lost son. The only way to save Gozo is for Bartlett and Jacques to find the Pasha's real son.