The peaceful city-state of Lisvalletta has recently been plagued by a new and dangerous drug called Anthem. This drug causes users to enter a state of Overdrive, where they mutate into superpowered beasts with inhuman abilities. Despite the efforts of the police, this new threat has proven too powerful for them to control. As a result, responsibility falls upon the Special Crime Investigation Unit SEVEN-O, which operates under the "Double Decker" system. This means that investigators work in pairs as "buddy cops."
As a child, Kirill Vrubel dreamed of being a hero who would save his school from a terrorist attack. His chance to become a hero comes when his landlady blackmails him into searching for her lost cat. While doing so, he finds himself caught up in a hostage situation involving an Anthem user. By teaming up with SEVEN-O detective Douglas "Doug" Bilingam, Kirill earns a spot on the unit and may finally achieve his dream of becoming a hero.