Area 51 the Reply

When they uncovered the truth about Area 51, scientist Lisa Duncan and Special Forces officer Mike Turcotte revealed the secret history of decades of UFO sightings and extraterrestrial contact. But that history goes back much further than they could have possibly imagined...
Hidden deep beneath the waters around Easter Island is a giant supercomputer called the Guardian, and it has just sent a message into outer space. When the reply comes, it will signal the execution of an alien plan millennia in the making; after five thousand years, "they" are coming back. But who are they and what do they want?
As the extraterrestrials race toward Earth, Duncan and Turcotte must scramble across the globe, from the Rift Valley of Ethiopia to an ancient Chinese tomb, to determine the aliens' true intentions. If they fail, first contact with these visitors could mean last rites for the human race.