Yang Ruyi (32), a fashion magazine photographer, lives with her elder sister Yang Ruxing (33), a rational, introverted detective fiction author. Ruyi has inadvertently photographed a couple making madly passionately love. Few days later in a shopping center not far from her home, she finds the woman already married, leading a child and is with a different man. Ruyi shares her secret with Ruxing who is suffering from writer's block. The two sisters begin to observe the couple; gradually Ruxing even writes some of her observations into her novel, without letting Ruyi knows it. Late one night, Ruyi views two people are arguing, but as she picks up her camera to photograph she can only see two vague, dark outlines wrestling one another; Ruyi calls the police but upon arriving, nothing seems out of order. Ruyi is convinced she has mistaken nothing; she enlarges the photo and discovers a third outline looks pretty much like her older sister...