七月（马思纯 饰）和安生（周冬雨 饰）的第一次相识在十三岁，她们一个是特立独行飞扬跋扈的“野孩子”，一个是单纯温婉循规蹈矩的“乖乖女”，从那一年开始，七月和安生几乎形影不离，她是她的光，她是她的影子，直到某一天，一位名为苏家明（李程彬 饰）的少年出现在了七月的身边，七月恋爱了。 　　安生决定前往北京讨生活，临别之前，七月意外的发现苏家明贴身带着的玉佩，竟然出现在了安生的衣领里。安生走了，七月和苏家明的恋情持续着，他们考入了同一所大学，约定一毕业就结婚。可是，事情并没有像七月所想象的那样发展，而她和苏家明之间的关系，亦因为安生的归来而产生了新的变数。30 year-old working woman LI ANSHENG's life in Shanghai is suddenly disrupted by the publication of a novel, entitled "Qiyue and Ansheng", a chronicle of her friendship with QIYUE during her youth. Coupled with an accidental encounter with SU JIA-MING, her long repressed memories are unleashed with the force of a tsunami-The two girls seemed destined to become friends from the moment they entered high school.Though they were inseparable and believed that their bond would last for the rest of their lives, the cruelty of youth eventually led them to separate paths. Even more shocking is the discovery of a long buried secret shared by the women - a secret that serves as an emblem of their youth and the proof of their friendship.