Roger Smith walks through a city that doesn't remember itself, and neither do you. The Big O doesn't explain the mystery, it becomes the mystery, each episode pulling you deeper into a noir that refuses to answer whether anything here is even real. The soundtrack doesn't score the show; it is the show, every synth line and jazz whisper telling you something the dialogue won't. By the end, you won't know what happened 40 years ago, and that's exactly the point.

Paradigm City is a place with no past. Forty years ago, some calamity wiped the memories of everyone living there, leaving the city full of forgotten histories and the ruins of what people built before. Now people born after that event are regaining memories of the old world and using them to create new threats, including giant robots and monsters. Roger Smith, a suave professional negotiator who dresses only in black, keeps finding that simple negotiations turn into fights to save the city from crime and danger. He is backed by Norman, his loyal and highly capable butler, and Dorothy, a humanlike android with a dry, deadpan wit. When things escalate, Roger turns to the Big O, a massive jet-black relic of a robot. As more memories surface and Roger digs deeper into the city's hidden layers, questions grow about his own past, Paradigm's future and what truly happened forty years ago. The series mixes mecha action with mystery and psychological sci-fi.