Patrick Le Brun caries on an oral narrative better than most podcast guests. His sense for mental-geographic timeline is excellent. The basis of his discussion is that neo-platonic thought and its practitioners hid within and piggybacked on the various Abrahamic faiths through the Middle Ages. I highly recommend this podcasts as an examination of how an all-submitting pan-national force—in this case Islam, but in our day also Atheistic Globalism—might be survived in the mind via the use of secret societies on the edges of the power structure and in the distant, barren places of the world.
The information on the Templers in his one digression is fascinating.
In the Walking Drum by Louis L’Amour the Hashishans make a crucial appearance.
For an historical survey of the intellectual life of early Islam, see When Asia was the World by Stewart Gordon
and A History of the Arab Peoples by Hourani.