Asako Morishita works as an undercover investigator for the authorities. Though you wouldn't guess it from her appearance, Asako has solved a variety of difficult cases. One day, she is given a document by her boss Toriyama. Written on the document is data showing that thefts of "mamachari" bicycles have been increasing in recent months. Asako immediately mounts her mamachari and begins an undercover investigation, exposing the organization of the theft gang, but at the hideout she reunites with the son of the devil, Kenji... and learns of the organization's plot beyond her imagination...