In Ashes Lie by Marie Brennan (2009) Hardcover

The year is 1666. The King and Parliament vie for power, fighting one another with politics and armies alike. Below, the faerie court has enemies of its own. The old ways are breaking down, and no one knows what will rise in their place. But now, a greater threat has come, one that could destroy everything. In the house of a sleeping baker, a spark leaps free of the oven -- and ignites a blaze that will burn London to the ground. While the humans struggle to halt the conflagration that is devouring the city street by street, the fae pit themselves against a less tangible foe: the spirit of the fire itself, powerful enough to annihilate everything in its path. Mortal and fae will have to lay aside the differences that divide them, and fight together for the survival of London itself . . .