Detective Sergeant Mariko Oshiro has been promoted to Japan’s elite Narcotics unit—and with this promotion comes a new partner, a new case, and new danger. The underboss of a powerful yakuza crime syndicate has put a price on her head, and he’ll lift the bounty only if she retrieves an ancient iron demon mask that was stolen from him in a daring raid. However, Mariko has no idea of the tumultuous past carried within the mask—or of its deadly link with the famed Inazuma blade she wields.
 
The secret of this mask originated hundreds of years before Mariko was born, and over time the mask’s power has evolved to bend its owner toward destruction, stopping at nothing to obtain Inazuma steel. Mariko’s fallen sensei knew much of the mask’s hypnotic power and of its mysterious link to a murderous cult. Now Mariko must use his notes to find the mask before the cult can bring Tokyo to its knees—and before the underboss decides her time is up....