In The City of Souls, the pilgrimage to the Valley of a Thousand Thoughts continues. Having already triumphed against dangerous adversaries in The Age of Akra, the four children - Mai, Long, Akra and Sahib - now face the evil melkarie and must escape to the City of Souls. When they reach the safety of the land of Naroan, in a city hidden under a blanket of living green, the children are confronted with the challenge of locating the Singing Soul. But the underworld is searching for it too, and will do anything to stop the young pilgrims from finding it. The prophecy is at risk of being extinguished unless the children succeed in their quest.