Must I hurt you in order to live?

The main character, 수안, is forced to make a choice between protecting her sister, 수련, and keeping the "ghost" called "그림자" from taking her life. "그림자" is a mysterious and ambiguous entity, unlike the more violent and active "귀신". 수안 and 수련 are sisters who live in a haunted house, and "그림자" demands that they each sacrifice one of their bodies to it. 수안, being the obedient sister, willingly offers herself to "그림자".

However, "그림자" then demands that 수련 be sacrificed instead, as she is the perfect match. As time passes, 수안 wakes up from a coma to find out that her sister has passed away. In a desperate attempt to save her sister, 수안 brings 수련's look-alike child, 재인, to their old home. "그림자" once again demands that one of the girls be sacrificed, but 수안 refuses to let her sister be taken. 금옥, 수안 and 수련's mother, is consumed by fear and decides to sacrifice 재인 to "그림자".

However, the curse of "그림자" is finally broken when 수련 sacrifices himself for 수안, showing that there is always an alternative to sacrificing someone. The movie ends with the realization that "it was not necessary to sacrifice anyone" and the possibility of a different path is explored.