I have never written down the answers to the deepest mysteries, nor will I ever...

The philosopher Plato wrote these words more than two thousand years ago, following a perilous voyage to Italy -- an experience about which he never spoke again, but from which he emerged the greatest thinker in all of human history.

Today, twelve golden tablets sit in museums around the world, each created by unknown hands and buried in ancient times, and each providing the dead with the route to the afterlife. Archaeologist Lily Barnes, working on a dig in southern Italy, has just found another.

But the thirteenth tablet is different. This tablet names the location to the mouth of hell itself.

And then Lily vanishes.

Has she walked out on her job, her marriage, and her life -- or has something more sinister happened? Her husband, Jonah, is desperate to find her. But no one can help him: not the police; not the secretive foundation that sponsored her dig; not even a circle of university friends who seem to know more than they're saying. All Jonah has is belief, and a determination to do whatever it takes to get Lily back.

But like Plato before him, Jonah will discover the journey ahead is mysterious and dark and fraught with danger.

And not everyone who travels to the hidden place where Lily has gone can return.