From the publishers blurb:
The persistent suborbital occlusion sits writhing in the west. It dropped from the heavens, some say, or maybe it bubbled out of the ground or burst out of the space between air, three years past. Some call it the shadow for how it negates the light, drowning everything it covers in opaque darkness. The sun no longer sets in the west: it disappears into the shadow, and each evening you can hear prayers at every hearth that it returns unchanged the next day. Most things that enter the shadow do not return, and if they do, they are seldom unchanged.