The play tells the story of a heroine who lost her favorite friend because of a serial murder case. After 19 years, she traced the serial murder case again and revealed the true face of the huge evil. Kim Seo-hyung plays the detective Cha Young-jin of the serious crime team. She did not protect her favorite friend when she was young, and she carried the guilt and remorse, and vowed to find the murderer. Yoo Deok-hwan plays the role of Lee Sun-woo, a science teacher at Shinseong Middle School. He was hurt as much as he poured his feelings into his students, and even more deeply. He wanted to leave the cult, but under the retention and persuasion of the people around him, he came to Shinseong Middle School where his brother-in-law was the chairman of the board. There he met a child with a passionate and warm heart.