Wizard and Glass

It is the fourth novel in the series and by far the longest—over 800 pages. Most of the book is a story-within-a-story: Roland tells his ka-tet the tale of his first love affair and his earliest days as a young gunslinger in the town of Hambry, decades before the events of the main series.

Susan is a young woman in Hambry who has been pledged to an older man against her will, and with whom the teenage Roland falls deeply in love. Their romance is the emotional center of the novel and one of King's most sustained love stories. Susan is widely considered one of the great tragic figures in King's universe.

After the flashback to Roland's youth ends, the ka-tet enters a world corresponding to a blasted post-apocalyptic Kansas and eventually encounters Blaine the Mono at Emerald City—an explicit parallel to The Wizard of Oz. The Dark Tower series engages throughout with the idea that all stories—including Oz—are shadows of the same mythology.

The Hambry flashback gives King the most extended canvas to develop a relationship in the entire series. Roland's love for Susan is not incidental—it explains why the adult Roland is emotionally closed, why he places duty above feeling, and why the cost of the Tower is so personal to him. King has said this book is the heart of the series.