A Face Like Glass by Hardinge, Frances-Hardback

In the underground city of Caverna, the world’s most skilled craftsmen toil in the darkness to create delicacies beyond compare—wines that remove memories, cheeses that make you hallucinate, and perfumes that convince you to trust the wearer, even as they slit your throat. On the surface, the people of Caverna seem ordinary, except for one thing: their faces are as blank as untouched snow. Expressions must be learned, and only the famous Facesmiths can teach a person to express (or fake) joy, despair, or fear—at a steep price. Into this dark and distrustful world comes Neverfell, a girl with no memory of her past and a face so terrifying to those around her that she must wear a mask at all times. Neverfell's expressions are as varied and dynamic as those of the most skilled Facesmiths, except hers are entirely genuine. And that makes her very dangerous indeed . . .