You Have to Kill Me

Police officer Chou is about to propose to his girlfriend Chen. He then receives a homicide case report and follows it to the mountain area. Sadly, the deceased is his girlfriend Chen. Devastated as he is, he tries his best and arrests the murderer Li. However, from Li's confession, Chou learns that Chen has voluntarily let Li kill her. Why do Li and Chen go on a murderous journey together? Or is it Chen who kills herself?