Woo Jin takes care of his son Ji Ho alone after his wife Soo A passed away. Before she passed away, she promised she would be back on a rainy day one year later. One year later, Soo A appears again, but she does not remember anything.

Hwang Ki Joon, Mr Action, and Kang Hee Yeol, Mr Bookworm, are two best friends but contradictory students at Korean National Police University. They accidentally witness a kidnapping and decide to work together to track it down.