The play tells the story of the heroine who lost her favorite friend because of a serial murder. After 19 years, she traced the serial murder again and revealed the true face of the huge evil. Kim Seo-hyung plays the crime squad detective Cha Young-jin, a character with a sense of guilt and psychological shadow because he does not guard his favorite friend. Liu Dehuan plays the role of Li Shanyu, a science teacher in Xinxing Middle School. He was hurt as much as he poured into his students, and even deeper. He intended to leave the cult, but under the persuasion and persuasion of the people around him, he came to the Xinxing Middle School where his brother-in-law was the chairman. There he met a loving and warm child.