A Scattering of Jades — Alexander C. Irvine

The great fire of 1835 burned most of New York City's wooden downtown and, like many others, Archie Prescott thinks he's lost all that's dear to him. His home is a smoldering ruin and his wife is dead--and next to her body is a child's corpse he assumes was his daughter. It seems as though it's the end of everything...

But it is only the beginning. In the midst of ancient magic, murderous conspiracies, and a crafty Mesoamerican demon-god who is plotting the end of humanity, Archie finds himself with the power to save the world--or drown it in sacrificial blood.