From wikipedia:


After celebrating a drinking party with his closest friends in Bangkok, Tun (Ananda Everingham) and his girlfriend Jane (Natthaweeranuch Thongmee) began to involve in a car accident. Jane hits a girl and Tun does not allow her to get down from the car. The couple drove away leaving the girl behind. Meanwhile, Tun discovers mysterious shadows on his photographs. Jane thinks that the girl who they hit on the road is haunting them while Tun dismisses the idea.Tun then begin to experience severe neck pains after the accident. Meanwhile, Tun's friends are also haunted by this mysterious girl and Jane begins to investigate about the girl. She finds out that the girl was Natre (Achita Sikamana), a shy and weird girl who studied with Tun in college. After confronting Tun, she realized that Natre and Tun were in a relationship. Tun kept their relationship a secret and when he broke up with her, Natre threatened to commit suicide. Tun and Jane then visits Natre's mother and they find decaying body of Natre in her bed room. They realized that Natre had committed suicide. Meanwhile Tun's friends have all being murdered by Natre and Tun feels that he will be the next. Tun is also then haunted by Natre. He almost fell from the building but survived. Jane meanwhile told Tun that Natre's funeral will be held the next day and everything will be back to normal. After holding the funeral, Tun and Jane returns back to Bangkok. Jane then discovers some photos and find Natre's shadowy figure in the pictures. She then finds that Natre is trying to reach something in the picture. She then finds some old photographs where Tun's friends are forcing themselves on Natre. Disgusted by the image, Jane leaves Tun. Tun meanwhile takes pictures with his shutter and in rage when he doesnt find her he throws the shutter across the room the impact of the shutter hitting the floor takes a photo of himself with Natre draped over his shoulders--which explained his neck pains and extra weight. He then jumps out of the building... Jane then visits him in the hospital and finds Tun in a critical state. At the end of the movie, we see Natre is still clinging on his shoulder meaning she will never leave him.