Kimihiko Kimizuka has been drawn to trouble almost magically since he was a young child. He had been to crime sites and drug deals so frequently that at one time even the police chief Fuubi Kase approached him with mistrust. He was even kidnapped one day and forced to leave the country with a briefcase containing unknown items. The master investigator Siesta was seated next to Kimihiko on the trip when it was discovered that the aircraft had been hijacked by the covert organization SPES. She promptly appointed him as her assistant. Together, they succeeded in capturing the hijacker and turning him over to the authorities.
That evening when Kimihiko got home, Siesta was waiting for him and wanted to formally appoint him as her assistant. After some early hesitation, Kimihiko eventually consented, and the two spent three years traveling the globe, occasionally engaging in perilous adventures and cracking innumerable cases. But when Siesta passed away, their trip came to a heartbreaking end.
Kimihiko resumes his semi-normal life as a typical high school student a year after Siesta's passing. His classmate Nagisa Natsunagi notices him as he solves a few criminal cases that occasionally drop into his lap and begs him to locate a particular person. However, this case poses a threat to upend his newly normal existence.