Morishita Asako works as an undercover investigator for the police. While her appearance might suggest otherwise, Asako has solved a variety of difficult cases. One day, her boss, Toriyama, hands her a document. It contains data showing that thefts involving "mamachari" bicycles have been increasing in recent months. Asako immediately mounts her mamachari and begins an undercover investigation, uncovering a gang of thieves. However, she soon finds herself confronted by the gang's son, who is hiding out at their hideout.