Detective Rosa White is about to convict the serial killer of Virbank when she stumbles upon a new clue about the activities of a mysterious crime organization. Her success gives her the opportunity to join the main division in Castelia, however this means becoming the mentee of the unpleasant Inspector Lack-Two. Can they overcome their differences and bust Team Plasma together?

In Victorian era Castelia, law student Rosa takes up the persona of master thief Whi-Two to afford her place at university, and eventually makes two acquaintances on one day that massively impact her life: Her fellow student Nate whom she quickly develops a crush on, and private detective Lack-Two, who is after her alter ego. Does he want her in prison or on a date with him?