When Shion, a privileged boy, gives shelter to an urchin for the night, the city he once called home forces him into the ghettos for insubordination. Four years later, an epidemic breaks out across the city. Shion, along with the help of the urchin Nezumi, must clear his name - even if it means

exposing the ugly truth behind the perfect city No. 6. Shion learns that his childhood friend Safu is under arrest and all because of him! Not wanting to get Rat involved, Shion sets out alone to save her. But how can he possibly infiltrate No. 6's secure correctional facility and escape with a high-priority prisoner all on his own?