Key Goes Through The Keyhole: Choi Seong-hoon, the deputy director of Sandeul Group's management planning team is in a relationship with Seong Jin-hee. However, he deceives himself as a soloist in order to get ahead and is dating Kang Min-joo, the only daughter of Sandeul Group's director and chairman. However, his operation fails when he starts to sneak with Jin-hee at the company workshop, and Kang Min-joo witnesses Choi Seong-hoon and Seong Jin-hee's love affair.