Strange rumors start to spread at the catholic girls' high  school after Unjoo committed suicide one night. Unjoo's  younger sister Jung-un who attends the same school gets  suspicious about Unjoo's death. After persistent  investigation, Jung-un finds out that on the night of  the incident, Soy, Eugene, Eun-young, Unjoo, the four of  them had tried to commit a joint suicide after making a vow  on blood. But the three are still alive, and only Unjoo had  died. the desire, jealousy, and lies behind the pledge of  death between the four girls are revealed, along with the  hidden truth behind Unjoo's suicide.