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...