The Father, the Son and the Big Brother
Despite the book's intended PMD premise, I still haven't ruled out the space alien theory. I'm not thinking of the almond-eyed grays of Close Encounters, but of the powerful creature in Star Trek V who masquerades as God.
Such a malevolent alien creature, one vastly more powerful and intelligent than us, wouldn't have much trouble performing enough "miraculous" signs to convince us it was divine. Those who believe that omnipotence is God's only significant characteristic would be especially susceptible to such a ruse.
Imagine that such a creature has been listening in on the radio signals beaming out into space from our little planet. For decades, those signals have included the prophecy babble of PMD radio preachers like LaHaye and Harold Camping. The creature realizes it has been given a step-by-step blueprint for how to steal away all of Earth's children for use as slaves in some nefarious intergalactic plot...
The evil alien posing as God is a far more interesting story, one I've pondered writing myself. It contains an intriguing philosophical problem: What would the world be like if the Bible were literally true? What would be the psychological effects of living in a society like ours, that is full of so much "Biblical Sin", to suddenly be confronted by a wrathful bearded figure with a host of killer angels at his disposal? How would it feel to live your life knowing that this same bearded control freak was watching everyone, all the time? Which made me realize just now that the world of the Biblical Literalist very closely resembles 1984 just with a a thin veneer of metaphysics.
In fact, such a hypothetical world would be worse than Oceania under Big Brother. Winston and Julia can at least entertain the fantasy, for a little while, that there is a place where Big Brother cannot see. In the world of LB, no such fantasy can be entertained. We all know that God is watching all the time, everywhere. It says so in the Bible. And that the smallest transgression of his neigh whimsical law would bring fireballs and plagues of locusts and Killer Angels to our doorstep.
I find it odd that so many Evangelicals fervently wish for this Biblical Tyranny, since that's what the Second Coming amounts to in PMD theology: 1000 years of Jesus in Jack Boots. A world where the mere thought of masturbating brings the flaming sword to bear witness to your physical damnation.
Of course, in my version of the story, there is a small band of Atheists who decide to sneak into heaven and kill God, freeing humanity from his despotic rule. They would have to contend not just with hoards of Killer Angels, but also blinkered Evangelicals who want the sadism of this world to remain, so they can watch with glee as their neighbors and relations are charbroiled alive for eating shrimp.