A Tale of Two Sisters (2003) ending / spoiler
Su-mi confronts her father about Eun-ju (the stepmother) locking Su-yeon in the closet. Confused and Frustrated, the father explains to Su-mi that Su-yeon is dead. The next day the father goes on an errand to pick up the person he's been confiding in on the phone. While he is away, Su-mi and Eun-ju have a violent showdown. The father returns to find a bloody Su-mi on the floor. He gives Su-mi pills, and she then sees the person her father brought to the house, a very different Eun-ju. Su-mi then realizes that the events that took place in the house since she returned were all in her mind, and that she was pretending to be Eun-ju all along. She is returned to the mental hospital where she reflects on the tragedy of her younger sisters death - a death that could have been prevented if she and the real Eun-ju had not had an argument.
Submitted by manicmuse