"Dinner at Deviant's Palace" (1985) by Tim Powers describes Greg Rivas's quest to save the woman he loves from a religious cult. Set in post-apocalypse California, where electricity and internal combustion are historical footnotes. Rivas is a redemptionist famed for freeing souls from the clutches of Norton Jaybush and his church. But he will have to go further than ever before to save Urania.
As in the best books the physical journey undertaken by Rivas mirrors a psychological journey in which he rediscovers himself. "Dinner at Deviant's Palace" is a journey into the heart of darkness, and Powers is familiar with various religious practices. It can be read as anti-religious. But I enjoyed reading it, good ideas and some good puns like the hemogoblin.