The book picks up immediately after the end of the first book, the Gunslinger. Roland wakes up on a beach, and is attacked by a small creature, which he labels a “lobstrosity”. He loses two fingers in his shooting hand, and a toe to boot. The wounds become infected, and Roland is rapidly losing strength. He walks along the beach and enters a door, standing by itself, labelled “The Prisoner”.
This allows him to enter the mind of a young man, Eddie Dean, who is smuggling cocaine into the USA from the Caribbean. When Roland’s help, Eddie manages to escape the clutches of the customs officials, and makes his way to the mob boss, who is holding Eddie’s brother until Eddie gets the cocaine. When Eddie discovers his brother is dead, a wild shootout ensues, which Eddie survives thanks to the superior skills of the gunslinger. At the end, Eddie joins the gunslinger on the beach, and they continue their journey.
At the second door, Eddie and Roland encounter a wheelchair-bound woman with dissociative personality disorder; Odetta Holmes is a mild-mannered civil rights activist, whereas Detta Walker is a violent predatory woman. Eddie and Roland have to contend mostly with Detta since Odette remains mostly suppressed. Roland becomes too ill to make it to the third door.
Odetta and Eddie enter the door on their own, and encounter Jack Mort, a sociopath who revels in hurting random strangers. He is responsible for the death of Jake Chambers from the first book, as well as for Odette losing her legs and having a split personality. Roland reaches and saves Jake, gets medicines and ammunition for himself, and kills Jack Mort in such a way that both Odetta and Detta witness his death, causing them to merge and become a new woman, Susannah. Now recovered, Roland, along with Susannah and Eddie, continue to the Dark Tower.
The first book was a prologue to the Dark Tower series, mostly just setting the stage. This book entwines the world of the Dark Tower with our own, and is written with a rich narrative replete with diverse language structures. The world building is wildly fantastic, and the three distinct characterizations all make this book an absolute joy to read.