Su-jeong, 19, has been living a hectic life, taking care of her deceased mother's belongings. She meets her first love, 'Black Flame Dragon', in a game she started by chance. However, her first love, which was full of excitement, ends up being the darkest part of her life... 16 years later, Su-jeong, who has become the team leader of Yongseong Department Store, meets the newly appointed head of the headquarters, Ju-yeon.

Su-jeong tries to repair her relationship with Ju-yeon, which was wrong from the start, but it is not easy. Su-jeong is just a thorn in Ju-yeon's side, who has a secret he does not want to be found out. Then, Ju-yeon eventually finds out about his private life and the situation changes.

A large-scale renewal project for Yongseong Department Store is underway, led by Joo-yeon. Joo-yeon and Soo-jeong grow closer as they work together. Joo-yeon's heart also opens up as Soo-jeong begins to understand him. But something happens that disappoints Joo-yeon in Soo-jeong.

Eventually, the 'Secret Room' opens. Soo-jung suddenly receives help from Joo-yeon. Joo-yeon's new appearance makes her laugh... Meanwhile, Shin-won does something he's never done before because of Ha-jin.

Ha-jin witnesses Su-jeong and Ju-yeon together. They must be separated before they realize each other's identity. Ha-jin's sabotage operation even involves Shin-won! Ju-yeon misunderstands that Su-jeong is interested in Shin-won...