The Dark Tower VII: The Dark Tower recap

In the final book the ka-tet is reunited but pays terribly for the Tower. Father Callahan dies covering Jake's escape from the Dixie Pig; Mia gives birth to the spider-child Mordred, who kills her at once and begins to stalk Roland's people. The company frees the psychic Breakers who are being forced to destroy the Beams, and in that battle Eddie Dean is shot and dies. Jake is killed soon after, saving the writer Stephen King from the van that would have ended the story. Grieving, Roland and Susannah go on; Susannah at last chooses love and life over the Tower and passes through a door into a kinder world. Mordred devours Randall Flagg, then dies at Roland's hand with Oy's help, though Oy is killed too. The Crimson King is erased from existence, and Roland reaches the Dark Tower alone, climbs it, and is thrown back to the desert where his quest began, doomed to walk the road again, this time carrying a horn that hints the loop might one day break.

So far, Roland Deschain, the last gunslinger of Gilead, has drawn and forged his ka-tet on the road to the Dark Tower: Eddie and Susannah Dean, brought from New York and wed, the boy Jake Chambers, twice bound to Roland, the billy-bumbler Oy, and their ally Father Callahan, a priest from another world. They destroyed the insane monorail Blaine, learned the tragedy of Roland's youth, drove off the dark sorcerer Randall Flagg, and defended the town of Calla Bryn Sturgis against the child-stealing Wolves. But Susannah was taken over by the being Mia and carried a demon-fathered child through a door to New York, and the fellowship split across worlds to save her and to protect the rose and the writer Stephen King, on whom the story of their quest depends. The great enemy, the Crimson King, works to topple the Beams that hold all worlds together, and the last stage of the quest is at hand.

Roland reaches the Dark Tower having lost everyone. Father Callahan dies at the Dixie Pig; Eddie is killed freeing the Breakers; Jake dies saving the life of the writer whose work sustains their story; Oy is slain defending Roland from the spider-child Mordred, whom Roland then kills though Mordred is his own monstrous son; and Susannah, unwilling to face the Tower, leaves through a door into a happier world where versions of Eddie and Jake live. Randall Flagg is devoured by Mordred before he can seize the Tower, and the Crimson King, trapped raving on a balcony, is erased from being by an artist's drawing. Alone, Roland enters the Tower and climbs to its top, where the door opens not onto triumph but onto the Mojave desert where his quest first began. His memory wiped, he sets out once more to chase the man in black, condemned to repeat the whole road. One thing is different: he now carries the Horn of Eld he once left behind, a small sign that on some future turn the cycle might at last be broken.