The world of the Dark Tower is set in ultra-distant, post-apocalyptic earth. Or at least could be. The Dark Tower itself is some sort of lynchpin that holds not just the earth or the universe together, but ALL of the earths and universes. The Dark Tower exists on an alternate world probably much closer to the world of the main character, Roland Deschain, than ours. The Tower holds the fabric of space-time together with six beams of an unknown energy that radiate out from its top. The effects of these beams can be felt through every world they pass through.

The story of TDT: WC unofficially starts more than 30 years before, when Roland is just a boy of 14. Roland is the son of perhaps the highest lord in his world, referred to simply as Mid-World. In this world, it's probably the year 3600 or more. Technology and civilization as we know it is gone because of some great, long ago catastrophe. But it isn't gone, there's electrictiy in some areas and artifacts of the distant past are everywhere. Craziest of all, magic exists in Mid-World, both in ancient artifacts and in powerful wizards. The highest nobles, like Roland's father, Steven Deschain, the Baron of Gilead (the seat of power in midworld,) keep power through military might and the very limited supply of guns. Only the highest men posess guns, and are like Jedi in practice. The Gunslingers, as they are called, are like the knights and lords of old.

But Gilead falls, as does the rest of the socio-politic structure of Mid--World, through the treachery of the man in black. The man in black is a powerful wizard who transcends space-time, and has the ability to affect not just Mid-World, but every world he freely travels to with arcane magic. The Man in Black, as he appears in Mid-World, goes under the name "Marten Broadcloak," and is Steven Deschain's court magician. Both Roland and his father are of the blood line of Arthur Eld, the original King of Mid-World dating back well over a thousand years. But Marten Broadcloak also possesses the knowledge of Arthur Eld's own magician, Maerlyn. (Yes, thats all obvious King Arthur references.) Marten senses that Roland's destiny is to save the Dark Tower. And Marten believes it is his own destiny to destroy the Dark Tower.

So through a convoluted method of treachery, Marten plans Roland's death and the destruction of Gilead, all while Roland is just a boy training to become a gunslinger. Marten seduces Roland's mother and eventually gets her killed. Also, Marten aids the Baron of another powerful nation, Lud, to discover the weapons of ancient man, things like flamethrowers, tanks, laser weapons, and high explosives. This Baron of Lud, known as John Farson, raises an army and marches on Gilead.

Roland and his other young noble friends come close to thwarting Marten Broadcloak. Before his father can send them all off for their own protection, Roland becomes the youngest ever Gunslinger by challenging his teacher to a duel to the death for the right to bear Steven Deschain's guns, which are enormous, .45 magnum calibur revolvers made from magical steel. He does this purely out of the desire to kill Marten for what he did to his mother. But he get's sent away to a neighboring barony and John Farson finishes his army.

While in Meijis, Roland discovers and once again nearly thwarts Farson's rebellion, but he was too late and far too outmatched. In the ensuing battle, every last gunslinger alive was killed by the technology of ancient man, but Roland escapes. He spends the next twenty years hunting down Marten Broadcloak, the man in black.

But at this point, Roland has a new purpose. Not long at all after the war, The Man in Black successfully starts his plan to destroy the Dark Tower. With the aid of demonic forces, as well as humans with powerful psychic abilities that he kidnaps from throughout space and time, Marten/the man in black successfuly snaps one of the Dark Tower's beams. Mid-World starts to slowly destroy itself like a person with cancer immediately afterwards.
So Roland becomes convinced his destiny is not to simply kill the man in black, but to save an artifact he grew up believing was a myth, the Dark Tower itself.

The intro starts with Roland now in his 40's. He's been chasing the Man in Black on foot across the world for nearly that entire time, always a town or two behind. Presently, he reached the edge of the healthy world and plunges headlong into the desert, relying on withs and survival skills to get to him.
Here is where the story starts becoming my own adaptation. But, still, like the books, whether it was on purpose or not, Roland successfuly reaches the man in Black along the coast of the ocean. The intro will be that rather anticlimatic showdown, and also the supernatural basis for how three random people from New York City end up in Mid-World fighting for the preservation of reality itself.