Chiyo, a 59 year old mother of 4, had lost her husband seven years ago. She will soon lose her home so she is offered by her eldest son, Ryoichi to live with him and his family. But her children are disappointed to hear that Chiyo has decided to become a live-in housekeeper. Then her eldest daughter Setsuko announced that Chiyo has had an offer of marriage. It is from the widower Kurosaki who had been a friend to Chiyo's deceased husband. Kurosaki runs a small company and has no children but has enough life savings. However, second daughter Tomoe, and youngest child, Yoko, are opposed to it. The siblings begin to argue. Meanwhile, Kurosaki tells his sister Namiko that he has decided to remarry. She is furious because he refuses to tell her anything about Chiyo. Thus, she takes it upon herself to find out about Chiyo and soon has a confrontation with her. Around that time, Kurosaki’s company is about to go bankrupt...
Kindaichi is off on yet another case, this time in Shanghai. When the father of a Chinese friend of the young Kindaichi is murdered at the circus, it is up to the ever-resourceful and clever young high-school detective to solve the case. But hidden in the background is the 4000 year-old legend of the Shanghai Mermaid.