Guy Psycho and the Ziggurat of Shame

Guy Psycho and the Postmodernaires don't have the credit to outlast the week when an enigmatic billionaire offers them five million dollars for a private performance of their lounge act.
Somehow, that performance includes re-enacting an ancient Assyrian epic deep inside a mountain in Tennessee, in the sub-basement of a mountainside mansion that leads all the way to ancient Mesopotamia.
To escape, Guy and his bandmates must retrieve a rumored thirteenth tablet of Gilgamesh. If they don't, they can't spend the five million, and worse, they'll be 5,000 years early for their gig at the Sabre Room.