Ji-won (Kim Ha-neul) is a bright young student with a promising future ahead of her. Her past however is a different story. Something happened to her a while ago, and whatever it was, it left Ji-won with a blank memory. She has no recollection of who she is, her friends or her life before the incident.

Hard work and lots of exercise – she enjoys swimming – has brought her back to her current state, almost completely recovered, except for the fact that she still can’t remember anything.

Ji-won’s plan is to travel abroad to study in the hope that leaving her familiar surroundings will do her some good, but her mother is against this decision. Ji-won’s father is dead, and her mother feels abandoned and alone. She tries to persuade her daughter to stay.

Ji-won begins to remember little things from her past that come to her in short flashes. At the same time she sees strange things around her: A little girl hiding in her closet, only to disappear the next moment, and dark figures looming in the shadows. She suspects that these scattered images and events are somehow connected to her past.

When one of Ji-won’s old friends Eun-seo (Bin) is found dead, drowned in her home, she begins to investigate her past. She’s desperate for any kind of information, but nobody will talk to her. Everybody seems to blame her for some horrible event.

Ji-won discovers that she was once friends with three other girls: Eun-seo, Yu-jeong (Jeon Hye-bin ) and Mi-kyeong (Shin-ee). Together these four girls formed an impenetrable alliance, and then… what? What happened? What did she do? Why does everybody look at her funny, and why – for the love of God – can’t she remember anything? Ji-won digs deeper into her past, hoping to find the answer. But as the old saying goes: Be careful what you wish for, you just might get it…