DESCRIPTION

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...

楊如儀（32歲），時尚雜誌的特約攝影師，跟姊姊楊如行（33歲），內向自持的推理作家，同住爸媽留下的老公寓，姊姊住五樓，妹妹因工作需要，住在頂樓加蓋的六樓。
某日上午，六樓意外飛來一隻金絲雀，楊如儀急忙拿起相機拍攝，卻在暗房沖洗照片時，發現自己無意間拍到了鄰近大樓裡一對男女激情做愛。
過了幾天，楊如儀在住家附近的購物中心，遇見照片中女人，她穿著樸素，牽著一個小孩，身旁男子卻非照片中人，楊如儀忍不住一路偷偷跟著他們。
楊如儀告知陷入創作低潮的楊如行此事，兩人開始研究、跟蹤這對男女。楊如行隱約比妹妹更樂於其中，甚至將偷窺內容寫入小說。某夜，楊如儀透過鏡頭驚見偷情房內有人扭打成一團後倒下，急忙打電話報警，警察來到偷情房間，但裡面看來什麼都沒發生過。
楊如儀堅信自己所見，她將手中的照片放大處理，赫然發現房裡的身影像極了姐姐...