To protect (actually, babysit) the most popular boy group of twelve gorgeous and flawless looking boys was their job. Get all the danger away from them, and make sure nothing happens to them. That was Girls' Generation's mission, as agents and spies. No affection and feelings must form during that period of time, but what will happen, when they suddenly fall for each other, and have to face their goodbyes once the mission finishes?

Just a small town girl, Im Yoona , who was always bright and cheerful, but not only that she had hidden talents and was very polite. After one day, after finishing college, she went to Seoul to pursue her dreams of becoming a member of one of the most famous korean girl group known as GIRLS GENERATION. Yoona finally, auditioned and was accepted by the companies manager. Until, one night she got a call from the companies manager telling them to meet up. When they both met up, the manager told Yoona that she is qualified to be one of the Girls Generation members, but she has to do something before becoming one of the members. The companies manager asked her to pretend that she was an Actress in training, and the manager asked her to live with 12 bad boys who are still in training, and their known as 'Exo', what happens when Yoona was asked to do a mission?, will she be able to pursue her dreams or will she leave Seoul and go back to her home town? or will she get a chance to take the opportunity and change the 12 bad boys to 12 flower boys? . Find out in the story.