Business is sluggish for the Ootsuji Detective Agency. Soutarou and his teenage sidekick Saki accept any job that comes their way, even those that appear to carry far more risk than reward. It is festival season in the city, yet away from public view, a series of mysterious disappearances has taken place. A newspaperman hires Soutarou to investigate, suggesting that answers may be found in the Dark, the notorious, anarchic maze that serves as the city’s physical, social, and moral underground. Soutarou subcontracts the assignment to Saki, but soon regrets the decision when the kid also goes missing. Now Soutarou is compelled to venture into the Dark himself, confronting its dubious subterranean inhabitants, including the malicious Laughing Masks gang and the renegade police squad piloting the fearsome Demon 463 armored train!