From the Flap:

Roland Deschain and his ka-tet are bearing southeast through the forests of Mid-World, the almost timeless landscape that seems to stretch from the wreckage of civility that defined Roland's youth to the crimson chaos that seems the future's only promise. Readers of Stephen King's epic series know Roland well, or as well as this enigmatic hero can be known. They also know the companions who have been drawn to his quest for the DarkTower: Eddie Dean and his wife, Susannah; Jake Chambers, the boy who has come twice through the doorway of death into Roland's world; and Oy, the Billy-Bumbler.

In this long-awaited fifth novel in the saga, their path takes them to the outskirts of Calla Bryn Sturgis, a tranquil valley community of farmers and ranchers on Mid-World's borderlands. Beyond the town, the rocky ground rises toward the hulking darkness of Thunderclap, the source of a terrible affliction that is slowly stealing the community's soul. One of the town's residents is Pere Callahan, a ruined priest who, like Susannah, Eddie, and Jake, passed through one of the portals that lead both into and out of Roland's world.

As Father Callahan tells the ka-tet the astonishing story of what happened following his shamed departure from Maine in 1977, his connection to the Dark Tower becomes clear, as does the danger facing a single red rose in a vacant lot off Second Avenue in midtown Manhattan. For Calla Bryn Sturgis, danger gathers in the east like a storm cloud. The Wolves of Thunderclap and their unspeakable depredation are coming. To resist them is to risk all, but these are odds the gunslingers are used to, and they can give the Calla-folken both courage and cunning. Their guns, however, will not be enough.