When unidentified parasites violently take over human hosts and gain power, humanity must rise to combat the growing threat.

A mysterious, justice-seeking entity throws chaos into the life of a cop who's willing to overlook ethics and corruption for a promotion.

Kim Seo-Jin (Shin Sung-Rok) is a man who is driven only to achieve success in his life. Thanks to his efforts, he is the youngest executive at his company. His life is perfect, with his beautiful violinist wife Kang Hyun-Chae (Nam Gyu-Ri) and a daughter. His wonderful life comes to a halt when his young daughter is kidnapped. He falls deep into despair. To change the past, when his daughter was kidnapped, he contacts Han Ae-Ri (Lee Se-Young) approximately one month in the past. Han Ae-Ri has busy days with her studies and working a part-time job to make enough money to pay for her sick mother's operation. One day, her mother suddenly goes missing. Han Ae-Ri falls into despair, when Kim Seo-Jin from the future contacts her.