From publisher blurb:
Travel in the Sea of Leaves is difficult and dangerous, especially when you seek to move through an area of the Deeps. Here the forest is so tangled that movement is near impossible, and it can take hours to travel only a few miles. Worse, the Call is strong in these areas of forest, and the unnatural expressions of the woods are more powerful where the trees grow thickest. Most communities do their best to avoid these areas. Most, but not all.
The west district of the city of Desburg is cut off from the rest of the city by ring of woodland Deeps, making overland travel in and out of this pocket extremely hazardous. However, there is another way. The Pipeline is a route under the choking forest, linking east with west. Now, the Pipeline is controlled by a community of ex-maintenance workers who allow scavengers through the tunnel, for a fee.