The story relates the adventures of Train Heartnet, alias the Black Cat, ex-member of Chronos Numbers, armed wing Number XIII of Chronos, an organization controlling a third of the world economy. He handles his Hades revolver to perfection, made of orichalcum, an indestructible material. After leaving the Chronos Numbers, Train allied with Sven Vollfied and became a sweeper (a bounty hunter). They quickly meet Rinslet (Rins), a professional thief, who asks them to help her with a mafia godfather's research on a young girl and "biological weapon" created by nano-machines: Eve. He will also have to face Creed Diskenth, his former teammate.
