Sometimes it seems like there are no Stephen King books left to adapt. His novels and short stories have spawned dozens of feature films, TV movies and miniseries, but King’s biggest fans know that there’s one massive story, one they’ve been dreaming about for decades, that still hasn’t made it to the screen: The Dark Tower.

King began writing his magnum opus—a fantasy spanning dimensions with all of existence at stake—while he was still in college, and he didn’t complete its main arc until 2004. All told, the eight-book series comprises more than 4,000 pages and more than three decades of King’s writing life. Over time, the saga began to not only grow in scope beyond any other King work; it actually began to consume his other work. King himself appears as a character in the story at one point, and there are thematic and plot-driven connections to other King titles ranging from The Stand to IT to Insomnia. It’s a sprawling, complex work of fiction, and the quest to get it adapted for film is almost as long and winding as the quest at the center of the plot. Now it finally seems to be happening, and two of Hollywood’s brightest leading men are at the center of it all.

After months of rumors, Entertainment Weekly confirmed today that Idris Elba and Matthew McConaughey have officialy signed on for a Dark Tower movie, which will be directed by Nikolaj Arcel (A Royal Affair) and will begin shooting in South Africa in just a few weeks.

Elba, fresh off a triumphant if lopsided awards season following the Netflix original film Beasts of No Nation (he collected SAG and a Spirit awards for his performance, and many felt he was snubbed for an Oscar nod), will play Roland Deschain, the hero at the heart of King’s story. Roland is the last Gunslinger, a member of a line of once-great knights King modeled on Western movie heroes. Roland resides in Mid-World, a place that has “moved on” and fallen into ruin. Being the last of his line, it is his duty to complete the quest to reach the Dark Tower. The Tower is a kind of nexus of all existence, and because the world is moving on, other worlds (including our own) are threatened. Roland feels he must reach the Tower to save everything from oblivion, and he will eventually team up with three heroes from our world: A heroin addict named Eddie Dean, a boy named Jake Chambers and an amputee named Susannah Dean (all of whom have yet to be cast). The journey to the Tower is a long one, full of danger, and though Roland’s world is crumbling, it’s still full of enemies.

Among these enemies is the Man In Black (McConaughey), a dark sorcerer who goes by many names and wears many faces. (He even appears in other King novels, including The Stand and The Eyes of the Dragon.) As the series progresses, it is revealed that The Man In Black has essentially conspired to bring down Roland and his family for most of Roland’s life, and that his ultimate goal is to claim the Tower for himself and become a kind of god-king. In the Entertainment Weekly report, King revealed that the first line of the film will be identical to the first line of the series, which crystalizes the relationship between the two characters: “The man in black fled across the desert, and the gunslinger followed.”

“It should start that way,” King said. “I’ve been pretty insistent about that.”

Though the film will start with the series’ opening line, King also noted that it won’t start with an adaptation of the first book.

“[The movie] starts in media res, in the middle of the story instead of at the beginning, which may upset some of the fans a little bit, but they’ll get behind it, because it is the story,” King said.

By the second and third books of the series (book three, The Waste Lands is a good bet for where the adaptation will start), Roland and his compatriots are spending time in both Mid-World and our world, and sometimes the two even seem to blend together in strange ways. With the right script, it could be a gripping dimension-hopping adventure. With the wrong script, it could just be confusing, but we’ll have to wait and see.

If you’re still not convinced that this news is a big deal, consider this: Oscar-winning director Ron Howard (A Beautiful Mind) and his producing partner Brian Grazer, one of the most powerful duos in Hollywood, have been trying to get this off the ground for six years. It was first set up at Universal Pictures, with Javier Bardem signed on to star and a plan to make a trilogy of films bridged with seasons of television (not such a weird idea now, but it was in 2010). Universal ultimately dropped the project, only to see Warner Bros. Pictures pick it up. Then Warners dropped it, and it seemed dead, until Sony Pictures re-invigorated the project last year, hoping to turn it into a franchise. For the moment, there are only plans for one film, but if it works, we could see more—including a TV series that might explore Roland’s earlier years (which are heavily covered in the fourth novel).

“They’re still holding on to this idea that they can do a TV series, and they’ve got it pegged for that,” King said.

If all goes according to plan, The Dark Tower will hit theaters on January 13, 2017, which is a remarkably short timeline, but for now King fans are just happy that it’s finally happening. The news was all capped off by this fun little Twitter exchange between the author and his two new stars. If you’re not a Tower fan, you might not understand why this is cool, but if you get it, you’re probably bouncing up and down in your chair right now.