Asher attached himself to a clan of salt miners who travelled deep into the desert near the border with Chad. His expertise as a former sapper in the British military was put to good use--he was a more skillful digger than his Sudanese companions.
What I remember most about the book was Asher relating how, because of the impoverished sensory stimulation of the desert's sameness, he was able to clearly follow single trains of thought for hours and hours without interruption.
I wonder if these same impoverished sensory conditions could have resulted in the delusions associated with the nascence of the three principal revealed religions--Islam, Christianity and Judaism?