Wizard and Glass (The Dark Tower, Book 4)

The Dark Tower IV

Part IV of an epic quest. Roland the Gunslinger and his followers have to contend with a sentient monorail intent on killing itself and taking them with it. While seeking to return to the Path of the Beam that will lead them to the Dark Tower, Roland tells his friends a story about the tragic loss of his first love, Susan Delgado. (source)