Wizard and Glass

The fourth novel in Stephen King's Dark Tower series is largely a flashback detailing gunslinger Roland Deschain's youth in the barony of Mejis. It chronicles his tragic first love for Susan Delgado and the events that hardened him. The story reveals crucial backstory about how Roland became obsessed with finding the Dark Tower.

Yes, it is essential to read the first three books, starting with The Gunslinger, because Wizard and Glass directly continues the cliffhanger from The Waste Lands. Roland is telling his backstory to his companions from the 1980s, so understanding who they are is crucial to the narrative. Stephen King published this installment in 1997.

It is actually both, as it heavily blends elements of high fantasy, horror, and classic western genres. The tale of Roland's youth in the barony of Mejis reads very much like a frontier western, featuring horseback rides and town standoffs. However, it is set in Mid-World and features deep magical lore.

Susan Delgado is Roland Deschain’s first true love, whom he meets while exiled to the coastal barony of Mejis as a teenager. Their tragic romance forms the emotional core of the novel's massive flashback. Her fate profoundly impacts Roland's character and his lifelong quest for the Dark Tower.