FAQ

No, the film is inspired by a Joseon Dynasty folktale entitled "Janghwa Hongreyon-jon", http://en.wikipedia.org/wiki/Janghwa_Hongryeon_jeon, which has been adapted to film several times. An American remake called The Uninvited (2009) starring Emily Browning and Arielle Kebbel as the sisters opened in 2009.

SPOILER!

The ghosts that keep appearing in the house are all of the younger sister, Soo-yeon. She does in fact haunt the house and is not just a complete figment of Soo-mi's imagination. The movie can become confusing trying to distinguish what events Soo-mi hallucinates with her multiple personality disorder, and what events actually occur. The ghost of Soo-yeon haunts Soo-mi for not being there to help her at the time of her death, and especially haunts Eun-joo (the stepmother) because she ignored Soo-yuen on the floor while she was bleeding-out to death underneath the dresser. The ghost of the younger sister Soo-yeon exists in this movie as BOTH a vengeful spirit that haunts the house, and as a mental projection of Soo-mi's to mask her emotional pain from the tragedy.

Now interpretation of the stepmother's repeated confrontations with the ghost is up to the viewer, as it is revealed that Soo-mi envisions herself as the stepmother, and Eun-joo in fact left the family after the death of Soo-yuen, thus meaning she was never there during the second visit of the house. However the ending sequence where it is implied Eun-joo is killed by the ghost of Soo-yeon hints at the possibility the stepmother might have been there during the second visit. Because Soo-mi wasn't at the house when this segment occurred which differentiates this scene from the rest of her projections. Real ghosts AND multiple personality disorder projected ghosts haunting the responsible Soo-mi and Eun-joo simultaneously? Once again certain events are debatable and are left up the viewer to decide. A bizarre and original plot that is executed very well, except is difficult to fully grasp on the first viewing. To those who caught on during their first viewing, kudos to you!