In this story, Sanderson returns to the world of Elantris. Sort of. He returns to the world, though not the same country, and though the magic system is similar, it's not exactly the same. Which is awesome, because as fans of Sanderson will tell you, one of the things he does best is to craft magic systems. Of course, he's also amazing at writing complex, interesting characters, and he's a master worldbuilder. Basically Sanderson is the sort of storyteller I aspire to be when I grow up.
But back to this book. It's the tale of Shai, a clever, but captured criminal who's tasked with the seemingly impossible task of Forging a new soul for the emperor in less than one hundred days. She also needs to find a way to escape, because once those one hundred days are up they won't need her anymore . . .
Don't worry if you haven't read Elantris. This great, fast read works wonderfully as a standalone, though I do recommend going back and reading Elantris too. And Warbreaker. And the Mistborn trilogy. And The Way of Kings. Start just about anywhere. With Sanderson it's nearly impossible for me to steer you wrong.
Here's a link to Sanderson's site. The man's very transparent about his writing process (he does also teach), so the site is a great resource for writers as well as fans.