Here is the briefest summary ever:
Book 5, Wolves of the Calla:
[spoiler]Roland, Susannah, Eddie and Jake arrive in a small town called Calla Bryn Sturgis, one of many small towns. Every twenty years, men disguised as wolves raid the town and kidnap one of every set of twins; for some reason the people in this town mostly have twins. The wolves, as it turns out, are due to arrive in a month. The townsfolk, which include Father Don Callahan, the priest from “Salem’s Lot,” who somehow slipped into this dimension, beg Roland’s help. Approximately 500 pages of talking later, Roland and the team kill the wolves, who are actually robots dressed as wolves who carry light sabers from Star Wars and grenades copied after the “snitch” from Quidditch in “Harry Potter.” No, really. The Wolves are being dispatched from somewhere in the East.
While all this is happening it turns out Susannah is pregnant with a demon child conceived in that battle where they got Jake. She is losing her mind again; now her other personality, obsessed with having the demon child, is named Mia.
They also simultaneously take many trips to New York City where they find that a bookstore owner, Calvin Tower, owns a plot of land on which the Rose, the anifestation of the Dark Tower itself, exists in New York. Tower is being leaned on by mysterious forces trying to get him to sell the land so the team plans to figure out a way to buy it themselves.
At the end of the book, the team kills the wolves and then Mia/Susannah escape to New York through a “Door.”[/spoiler]
Book 6, Song of Susannah:
[spoiler]The team chases Susannah back to our world, sort of. Callahan and Jake go after Susannah and rescue her although the demon child, Mordred, is born. He’s a big spider. Callahan dies in the effort.
Roland and Eddie head off to Maine to pursue Calvin Tower, who has fled there to escape the gangsters hired by evil forces to get the vacant lot the Rose sits on. (They’re the same gangsters Roland and Eddie killed in Book 2; they entered our world 10 years before that.) However, they also go after… Stephen King, who they believe to be key to all this because they found a copy of “Salem’s Lot,” the bok Callahan was in, and were amazed to discover one of thei number in a novel. As it turns out, Stephen King is God, and he created them by writing “The Gunslinger.” No, I’m not shitting you. Roland hypnotizes King and tells him to keep writing Dark Tower books. Really, I’m totally serious.[/spoiler]
Book 7, The Dark Tower:
[spoiler]A lot of boring shit happens, but basically they get to the place where the Beams are being broken by “Breakers,” ESP-heavy folks gathered by the evil Crimson King to break the Beams and destroy the Tower. They slay all the minions of the Crimson King and chase the Breakers away, but towards the end of the battle Eddie is shot and dies.
They then have to go back to New York and Maine for some reason and save Stephen King, who is of course God, from being hit by that truck. Jake, trying to save King, is hit by the truck and dies. King/God is badly injured, just as he was IRL.
Roland and Susannah go back and continue going for the Dark Tower. A lot of boring shit happens. Eventually, Susannah, heartbroken over Eddie’s death, kind of gives up; she has a chance to go back through the “Door” to New York, and does so. Roland goes on with Oy, Jake’s billy-bumbler.
Roland finally encounters Mordred the demon child spider thingy, and kills it. Oy dies in the battle. Roland goes back to New York (I may have this out of order) and a big company headed by Susannah’s relatives has bought the vacant lot.
Roland finally gets to the Dark Tower. The Crimson King is a big fat guy who squeals like a pig and throws grenades. Roland, with the help of some kid they picked up along the way named Patrick, defeats the Crimson King by having Patrick erase him in a picture. He marches triumphantly into the Dark Tower.
Susannah arrives in an alternate dimension New York. Eddie and Jake are waiting for her; they don’t remember her, but were drawn to her arrival.
Roland climbs the steps of the Dark Tower, steps through the door at the very top - and winds up back at the beginning of the first book, chasing the man in black across the desert. The only difference is he has Cuthbert’s horn now for some reason.