Okay it seems everyone is confused what happened at the end and maybe that was the writers intention but here is my theory. Rebecca, the girlfriend, is lucy. She was with a man called ben and was pregnant but left him to be with alice. Alice was extremely jealous and accused lucy of having an affair with ben. She then tried to drown her in the bath and killed the baby (but not lucy). She has repressed this event. While in the house she re-lives the past only this time she is the victim not the perpetrator! She lives through what she did to her girlfriend lucy. When lucy gets to the house and sees alice has had a breakdown she promises she wont leave her again (as she was about to leave the house when alice drowns her). She then sees her own necklace on alice neck. Later she sees she has wrote a book using the characters lucy and David. When lucy sees the video tape she is watching real footage of herself and alice (who is David!) Is that clear? The conversations alice has with ben and rebecca are in her head. In seeing the movie with this explanation i think it is really clever.
Review of Deadline
