If you're inclined to have a Greek mythological spin on things you write, Jane Ellen Harrison is a great author to consult on early Greek ritual religion. I've just started reading her Prolegomena as I research for a curriculum. Far from the usual research one might pursue in Greek mythology (particularly for fiction: i.e. what color eyes does Athena have, for whom is each moon of Jupiter named, et cetera), she observes that by the time we get to Homer (the common starting place for Greek myth and literature studies), the Greek religion was practically postmodern, the gods all but swept into the background of significance except for how a sacrifice might bend their erudite whims to your cause. Interestingly, as you push back further, you find a Greek world where the gods are held at bay more than made your friends.

Greece is so often viewed as the apex of culture that it's rare to see fiction delve into the nightmares of the early Greek pagan mystery cults. Wouldn't that be an interesting change?