 When we meet Eileen, we see her sabotaging her big sister s wedding. We find out that she blames her older sister, Claire for a car accident that has left her deaf and mute. As Eileen tells us the story from her perspective we see a series of flashbacks that tell us about a love affair that she had with her sister s groom James. They had kept the relationship a secret due to an age difference, from everyone except Claire. When James won t believe Eileen s story about Claire trying to murder her, she sets her plan into motion and swears revenge on the newlyweds. As we watch her try to ruin Claire s big day, the audience is left guessing if Eileen s story is the truth.