A disastrous great flood sweeps the planet. On what may be the last day on Earth, a desperate fight ensues to save a child from a flooding apartment.

A great flood has hit planet Earth. People, including An Na and Hee Jo struggle to survive in their apartment building, which is sinking into the water. An Na is an AI development researcher and Hee Jo belongs to a human resource security team, who is trying to save An Na from the disaster. But why is Hee Jo trying to save An Na and who is behind it?