David Nessio faced plenty of danger in Syria, doing rescue archaeology in the midst of a civil war. Back in Washington, DC he thinks he is safe and can get back to his graduate studies. But a phone call from a stranger leads to him to the scene of a murder, and from there he descends back into violence and peril. Something his team found in Syria is so valuable, or so dangerous, that people would kill for it. As Nessio tries to figure out why, he keeps being pointed back to the period of history called the Bronze Age Collapse. Prayers from that time, around 1200 BC, lament that humans have lost contact with the gods and their messengers. Nessio learns that there is an idea, passed around among believers in secret, that we used to know how to reach the gods whenever we wanted. People call this knowledge the Key. Nessio discovers that while many believers are desperately seeking the Key, so they can bring divine power back into the world, others are equally determined to stop them. Nessio can't believe in any of this, but since people on both sides are certain he knows something important, perhaps even the Key itself, he is drawn into their shadowy conflict. He travels across the US, then to Germany, and finally back to Syria, where Key believers try to open a door to other worlds in the ruins of an ancient temple, and sinister powers move to stop them.