Hyun-heup, a girl who was born with the ability to see the S-line that indicates sexual relations. Because of this ability, Hyun-heup's family faces tragedy, and Hyun-heup becomes a reclusive loner for a long time. Then one day, a series of suspicious murders occur around Hyun-heup, and Hyun-heup uses his ability to see the S-line to track down the case...

Hyun-heup goes to Bangju High School after receiving a mysterious text message. There, he reunites with Seon-ah, a middle school classmate and Ji-wook's niece. However, Seon-ah is a victim of bullying from bullies. One day, when the bullying from bullies reaches its peak, Seon-ah discovers a mysterious pair of glasses in her locker...

Seon-ah falls from the rooftop and falls into a coma. Ji-wook cries out in self-reproach and anger, and cooperates with Hyun-heup to find the culprit. Meanwhile, Jung-woo, an English teacher at Bangju High School, witnesses his girlfriend's affair before their wedding and breaks off the engagement. And soon after, he finds a pair of glasses on his desk...

Ji-wook, who was continuing the investigation to find the culprit of the Seon-ah incident, hears about the S-line from Hyun-heup, but doesn't believe it. Meanwhile, Bang Ju-goo, an employee who lives in a goshiwon and dreams of becoming an actor, finds S-line glasses at Mi-seong's house and feels liberated, but soon after, he sees a woman connected to the music teacher he had a crush on and feels strong jealousy...

Ji -wook, who finally discovered glasses in the bloody bathtub of aesthetic, admits that the words of Hyun -suk were true. Use the power of glasses to start an investigation into sexual violence in the runway. And I think that the person connected to the only one S line of Sun -ah is the culprit of the Sun -a case.

Ji -wook finds out the truth about Sun -ah's S -line through glasses. Meanwhile, Hyun -suk, ahead of his 18 -year -old birthday, makes a big decision and meets the Jun -sun, which leads to an unknown confusion.