Roland, Jake, Eddie, Oy, and Susannah continue on their journey to the Dark Tower when they are followed by a group from the town Calla Bryn Sturgis. A town where singletons are rare. Every few decades, "wolves" come to the callas and kidnap a twin. The twin is returned "roont" (their term for mentally handicapped). They turn to Roland and his ka-tet in hopes that they can save them from the wolves once and for all. While all of this is occurring, Susannah is going through her own struggles. More mysteries arise as others are solved. Can Roland save the people of Calla Bryn Sturgis? 
This is full of twists and turns and loveable people. The detail is grand and Stephen King proves once again how masterful of a storyteller he is. The books make references to Harry Potter, Wizard of Oz, and Star Wars, among others which I found amusing. I can't wait to continue the series.