Roger Smith is Paradigm City's top Negotiator. He solves all sorts of problems for all sorts of peoples. And when things get rough he's got some pretty big back-up: The Big O, a giant robot from an era long gone and forgotten.
Together with his faithful servant Norman and the android R. Dorothy, Roger defends Paradigm City, a city that has lost its memory after a mysterious event some forty years earlier. And Paradigm City needs a lot of defending. Fragment of Memories appears, and where they do, trouble follows. There are rogue robots, monstrous creature, and seemingly invaders from another land, and the Big O is Paradigm City's last line of defense.
But as they battle these monsters, Roger and the others gradually uncover pieces to a bigger puzzle. A puzzle that someone doesn't want solved.