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...

Why on earth did they kiss? Soo-jung is embarrassed by what happened last night. She believes that Joo-yeon will confess or explain, but Joo-yeon doesn't say anything. Soo-jung, who is upset, decides to go on a blind date with Ha-jin.

Juyeon doesn't hide his feelings for Sujeong. However, Sujeong rejects him due to the 'younger man' trauma. Then Juyeon is about to get caught by Hyoseon.

Soo-jung and Joo-yeon finally confirm each other's feelings, and their thrilling secret love begins. It's a love that must be kept secret from everyone, but they're happy that they can be together... What is this ominous feeling? Meanwhile, Shin-won and Ha-jin have a chance meeting at a wedding hall