A string of mysterious deaths has occurred, leaving all of the victims with a purple butterfly-shaped bruise. According to investigators, the victims have all died from a hypnotic suggestion. The police bring in renowned psychiatrist Toshiya Saga, who specializes in hypnotic cures, to help with the investigation. He is determined to solve the mystery, but is caught off-guard when the woman he is attracted to becomes a suspect in the investigation.

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.

A ryokan maid is on trial for pushing a familiar guest off a cliff to his death. An eager attorney offers to take the case to gain notoriety.