Ignatius and Indigo find themselves struggling mentally to come to terms with the complex nature of the cosmos and their newfound supernatural powers obtained through their prior encounters with gods and demons. In their quest for another relic from the Creation, they are aided by the secretive thirteenth Chapter of the Union Jacks. In search of the secret of the Flaming Celestial Pearl, they must travel to Tibet in the great airship, HM Spirit of the Empire.

Pursued by fanatical knights sworn to protect the relic, they must reluctantly call upon the Charon, the seven merciless demons from the underworld to assist them. Piecing together the map that will lead them to a fabled city hidden deep within the Himalayas, they must defend themselves from air pirates, a previous foe from Oxford, mountain beasts and elementals.

Discovering the correct path through the mountains, Indigo realises her soul may never be the same again. Regardless, they enter the Great Void where using the Sword of Wisdom, they discover the truth about the cosmos.