General Wang Sheng (Kun Shen) atacks a bandit camp and saves Xiaowei (Xun Zhou) who is a demon fox spirit that needs to feed on human hearts to keep her nice appearance. Wang Sheng brings her home and presents her to his wife Pei Rong (Vicky Zhao) that welcomes her and offers to keep her in her service. But Xiaowei falls in love with Wang.
Strange events then happen, including people disappearing or dying, so Pei Rong turns to a demon hunter, Pang Yong (Donnie Yen), who is tired of things and not of much help. He meets an inexperienced demon hunter, Xia Bing (Li Sun) who is very interested in the events, and thinks a chameleon demon is the cause of problems. It is indeed such a demon, Xiaoyi (Yuwu Qi) that is in love with Xiaowei and kills people to bring her hearts.
Pei Rong won't quit finding the source of problems and confronts Xiaowei that reveals her demon form and forms a pact with her : the killings stop, but Pei Rong takes the blame for the murders.
This is a mix of faery tale, Wuxia and love story. The main cast does a breathtaking job, creating powerful characters with strengths and weaknesses, and led by their emotions and honor, including the demons. This makes a very moving story, as noone is really guilty and tries to hurt as few people as possible, or at least believes they're doing the right thing. I've been a fan of Vicky Zhao for years, and Donnie Yen is always great, but it's Xun Zhou that really shines here. Her mysterious charm creates a complex and charming character that we try to hope will either become good or be forgiven for her actions.
Very recommended.