It's the year 2636. In this time period, new planets and aliens have been discovered, there hasn't been a war on Earth for 400 years, you can cure a common disease with a simple pill, and technology can expand the human life span to 150 years. Everything is at peace. Until one day, when the Tetra, a highly advanced alien race of blue people, go to visit Earth only to find everything and everyone on Earth is gone. Lands once filled with fields of tall grass have become nothing but dust and dirt. Largely populated cities have been turned into crumbles of rock and concrete.

Then, they find Amber, a young girl who turns out to be the only human left. To the Tetra's dismay, it turns out Amber has amnesia so she can't remember the disappearance of the humans. Since she has nowhere to live and no family, a Tetra elder takes her in as their child. As Amber becomes older, her memory starts to come back and she soon finds out she has something to do with the disappearance.

Now, the Tetra depend on Amber to solve the mystery, for they might be next…