Infernal Sorceress was Gary Gygax's final novel, and it sat unpublished in his files for almost fifteen years before Planet Stories got a hold of it. Set in Gygax's world of Aerth (the setting for his Dangerous Journeys RPG), the novel introduces two new characters: thief/swordsmen named Ferret & Raker. After being framed for murder, Ferret & Raker become pawns in a political power struggle involving fake royal regalia and have to keep one step ahead of the authorities while discovering the true villains involved.
TSR refused to publish the novel on the grounds that it was a swipe of Fafhrd and the Gray Mouser, and one can definitely see the inspiration. On its own merit, the novel is passable but unremarkable sword-and-sorcery. Neither the characters, dialogue, or plot are particularly memorable. One can definitely imagine having a lot of fun playing through the adventure in a role-playing game, but as a standalone novel, it simply falls flat. I think Gygax's other novels set in the same world, involving an arcane detective named Magister Setne Inhetep, had much more interesting characters and portrayal of magic (even if Gygax was a poor mystery writer).