The Tag-Along: The Devil Fish is a famous folk tale in Taiwan about creatures such as fish with human faces. Which group of people involved a temple priest, a boy and his mother haunted by an evil spirit carried by a captured fish.
Lin Zhi Cheng (Cheng Jen-Shuo) is a local priest who has the ability to be able to ward off evil spirits that enter the human body. A fifth of his colleagues from the police department came to ask for help so that he could get rid of an evil spirit who had entered a man who killed all his family from the cruelty of the creature.
While Jia Hao (Chaster Wu) is a young man who along with his friends are working on a short film related to the supernatural for competition in their school. At that time they were together to be able to investigate about the exorcism of evil spirits by Master Lin through the media of fish.
Master Lin tried to be able to drive away from the evil spirit that had possessed the man and also Jia Hao who along with his mother (Vivian Hsu) who were then terrorized by the Devil Fish that was born after frying the Devilfish in the exorcism of the evil spirit.