An underrated novel that deserves critical reexamination, Philip Jose Farmer's 1966 book, Night of Light, is a powerful treatise of one man's redemption and the overwhelming influence of religious belief. It's also a pretty good mystery thriller as well.
Set up in two parts, Night opens with the events on the planet Kareen (AKA Dante's Joy), where the inhabitants every seven years prepare for the "Night", when the planet undergoes a bizarre manifistation. (This is somewhat similar to the situation described in Isaac Asimov's classic short story, "Nightfall".) The planet's skyline becomes a "purplish haze" (yes, this is the book that Jimi Hendrix reportedly was influenced by) and the people have a choice of either entering a drugged sleep ("the Sleep") or partcipating in a bacchanalia-like orgy of psychedelically-delineated destruction.
In the middle of all this is John Carmody, one of the most reprehensible protagonists the reader will ever meet (at first). A sociopath, Carmody is haunted by visions of the wife he murdered during the Night. But that doesn't stop him from planning to murder the planet's human god Yess. However, the followers of Yess (who represent Good), his goddess mother Boonta, and Yess' brother Algul (Evil), all have their own agendas to follow. And their aformentioned respective agendas all involve Carmody's services, so to speak.
And that's just the first half of the book! What follows involves religious and mysterious intrigue, various hallucinatory sequences, odd bits of business (like one character transformed into a tree), and the transformation of Carmody from conscienceless mercenary to.. But to say more would spoil the whole thing.
As noted, the novel is split in two parts, with the first half Farmer's original 1957 novella, and the second part (set twenty-odd years later after the events of the first part) was written expressly for the book. Farmer's writing is somewhat experimental in the first half, with its stream-of-conciousness tone, and more linear and self assured in the second, yet both halves cohere seamlessly. Though obviously concerned with providing a compelling narrative for his readers, Farmer nevertheless opens the door to asking questions about the power of Faith, whether all religions are inter-connected, and the pluses and minuses of unconditional belief. You'll find Night of Light worthy of a second or third read just to make sure you didn't miss anything the first time.