Paradigm City, a futuristic metropolis, has lost its past. A mysterious occurrence, known only as "The Event", has stolen the memories of the city's denizens and left them under oppressive police rule. While Paradigm City's collective population struggles to remember their past, Roger Smith, a "Negotiator", seems to have a connection to the city's past and sets about investigating this mystery. With the help of the Big O, a crime fighting robot suit, Mr. Smith searches the underbelly of the city for an answer as he tries to uphold his sworn duty to protect the populace.