Magic and the Shinigami Detective

When the Night Foxes boldly break into the Fourth Precinct’s Evidence Building, it causes quite the stir. The break-in is daring enough, but their method shreds the magical wards and protections on the building like confetti paper. To say the police are ‘alarmed’ by this is the understatement of the century.
As a Magical Examiner, Henri Davenforth is of course immediately called in. Quite to his astonishment, Captain Gregson has him work the case like a detective. Even more astounding, he assigns Henri a partner.
The Shinigami Detective.
The woman is famous for killing the most destructive rogue witch of the century, and no one is quite certain where she’s from. Every officer in the precinct is either in awe of her or a little frightened by her. Henri is just baffled. What is he supposed to do with a partner?
Hopefully killing one witch makes Jamie Edwards enough of an expert on magic to be helpful, as the thieves aren’t content to just break into one building. They in fact seem to have an agenda, as with each theft, they take magical objects. It’s all mounting to a dangerously powerful magical construct capable of toppling the wards on any building.
And no one has any idea what the thieves’ true target is.