Kim Yongsun is the best secret agent in her company, or she is just the one who looks young enough to pretend to be a high school student. She was sent to the usual high school to steal secret files. But beforehand Yongsun has to get close with Moon Byulie, the potential owner of the files.

"Of course I'm in," Yongsun immediately agrees.

She has no doubt that it would be the easiest mission she has ever had.

If she only knew how wrong she was.