Alloy of Law

Alloy of Law is set 300 years after the previous Mistborn novels. The world has continued along since the final events of "Hero of Ages". The world is somewhat similar to our world, though with some key differences. The "magic" is present, but in a lesser degree than in the early novels. All this provides the basic setting for a crime novel.

Some people have been mysteriously robbing train shipments. Eventually they start taking other things and eventually are taking hostages.

The crime fighters had previously worked out in the "roughs", but have now returned to "civilization. Waxilliam is part of a noble family on hard times who has two powers, while Wayne has the ability to "speed time".

Eventually they solve the crimes but find the mastermind behind it all is an unexpected relative.

This seems like something that was fun to write. Sanderson had this nifty fantasy universe created and then said "hey, what if I throw in a crime story here." It made for a fun book, and leaves plenty of loose ends to continue if he still maintains the interest. If not, he can start exploring elsewhere.