A great flood hits planet Earth. People, including Gu An-Na (Kim Da-Mi) and Son Hee-Jo (Park Hae-Soo) struggle to survive in their apartment building, which is sinking into the water. Gu An-Na is an AI development researcher. Son Hee-Jo belongs to a human resource security team and he is trying to save Gu An-Na from the disastrous situation. Why is Son Hee-Jo trying to save Gu An-Na and who is behind that?