This work tells the story of Ibuki Ai (played by Ayano Tsuyoshi), who is second to none in the police \”mobile search team\” in maneuverability and motor nerves, but has no criminal investigation experience and lack of criminal common sense. He has outstanding observation and social skills, but does not trust himself. A story with the rational detective, Shima Kazumi (Hoshino Gen), and the two protagonists aiming to solve the case within 24 hours. The \”MIU\” in the title is the initials of the Mobile Investigative Unit, and \”404\” is the call signal for two people to play the mobile investigative unit.