In the year AD 1054, a wise man from the Chaco Society scratched an ominous warning in rock art. More than a thousand years later, twenty-six-year-old tribal archaeologist Jon Two-Bears and professor Pamela Parker team up on a dig in the west end of the Grand Canyon. To their surprise, they uncover what appears to be an ancient warning. It predicts there will be a huge landslide in the narrows of Lake Mead that will send a freshwater tsunami downstream eighteen miles—wiping out the Hoover Dam. The inland tsunami will continue south, destroying everything in its path to the Gulf of California. Due to the seismic activity that is taking place in the Lake Mead area, it's obvious that this ancient prophecy is about to become a reality.

Jon and Pamela make a valiant effort to convince people to flee to higher ground before the killer waves wipe out large areas of the southwestern United States. Will the warnings be heeded? Or will millions become victims of the tsunami twins?