After her fiancé Joseph (Aloys Chen) falls ill, Bobo (Jiang Yiyan) meets a mythical being who offers her a chance to become a butterfly for three years in exchange for his successful recovery. Unsurprisingly she accepts, but when he recovers from his illness, Joseph is struck by the disappearance of Bobo. Just as the end of her pact draws near though, a plague spreads across Celestial Island. When Bobo realises her butterfuly form may hold the key to the cure, she goes on a journey to seek the truth. Meanwhile, Joseph’s neighbour (Kwai Lun-mei) and a visiting journalist (Gigi Leung) are both trying to persuade him to move on with his life and settle down with one of them.