This story is also Chapters 7-11 of To the Land of the Living. The title is a phrase borrowed from Conrad's Heart of Darkness.
Other resources
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Acknowledgements: Robert Silverberg for cause, support, and cooperation; Ken Seamon for graphics; Rodney Walters for books and info; Alvaro Zinos-Amaro for comments and content; and all the fellow fans who have sent encouragement, information, and translations.