When programmer Yuan Ming accompanied his pregnant girlfriend Chen Shishi to a prenatal check-up, he unexpectedly discovered traces of his ex-girlfriend Han Yan, who had been missing for four years. Four years ago, Han Yan left without saying goodbye without any warning, just like evaporating from the world, leaving a huge mystery in Yuan Ming's heart. Now, like a ghost, Han Yan reappears "just in time", like a key, about to open the door to the dust-covered past, allowing all the truth to gradually emerge. Why did Han Yan suddenly disappear without a trace? What happened to her best friend who always exuded a frightening aura? And what kind of unknown identity does Chen Shishi, who is accompanying her in front of her, have? As the truth is revealed step by step, Yuan Ming seems to be on the edge of an abyss, and his world is about to collapse.
