[1][2][3] It revolves around the story of four women in their 30s and their complex relationships - each on her own path to self-discovery as they brave the turbulent journey together.

The series starts with close friends Se-Yeon (Han Ga-In), Eun-Soo (Shin Hyun-Been), Jung-Won (Choi Hee-Seo), and Hwa-Young (Goo Jae-Yee) standing in front of a dead man's body.

Sun-Ho vows to kill this mistress, hinting that he is aware of Eun-Soo's relationship with his late father.

One day, a female client comes and requests that someone secretly follow her husband Tae-O (Kim Min-Soo).

The first script reading was held on March 15, 2018 at Studio Dragon's main office in Sangam-dong, Seoul, South Korea.