JK Rowling's new 'Harry Potter' movie is doing the one thing that makes spin-offs work

When JK Rowling published "Harry Potter and the Deathly Hallows" in the summer of 2007, it was the end of an era. For Harry Potter fans, there were a few movies left to look forward to, and then it looked like the deep well of the Harry Potter universe was about to run dry.

Fortunately, Rowling had a solution of her sleeve: a spin-off.

In November, "Fantastic Beasts and Where to Find Them" will be released. It's the first in a trilogy of movies, and Rowling wrote the screenplay herself, unlike with the "Harry Potter" movies.

The story will center on Newt Scamander, a magizoologist who comes to New York. But Rowling isn't just telling the story with the movies, she's taking advantage of her formidable Twitter feed and of Pottermore to tell the story of American wizardry.

The most important thing Rowling did was to set the story in 1926 and in New York.

With this approach, Rowling nailed how to do the perfect spinoff: change the setting and focus on new characters. That way, the rich world of Harry Potter still exists. But Harry Potter himself - nor, for that matter, most of the other characters in the series - can show up to distract us.

To be sure, some characters might show up. Albus Dumbledore, for example, was born in 1881. He's like the oldest person ever, so he can very well show up in "Fantastic Beasts and Where to Find Them." But even though Michael Gambon, who played Dumbledore in most of the films, wants to be in the "Fantastic Beasts" movies, Rowling hasn't said anything about him showing up.

The connections between the original "Harry Potter" series and the American magical world still explicitly exist, though, and that's what makes it fun.

"Fantastic Beasts and Where to Find Them" is a textbook Harry uses in his Care of Magical Creatures class in his third year at Hogwarts, taught by Hagrid. The author of that textbook is: Newt Scamander.

Rowling published the book herself in 2001. It's an encyclopedia and guidebook about magical animals.

She a similar approach for her new short story about the history of Ilvermorny, the American wizarding school.

For years, Rowling released new information on Pottermore, a site she launched in 2011 that contained new information about her magical world, with more details about the characters we already knew.

But the story was over. Pottermore was originally like an encyclopedia, not a narrative. The details were interesting, but not gripping.

That's why the new story about Ilvermorny works so well: it's a story.

And the story clearly takes place in the same universe as the rest of the Harry Potter series. Some of the same names referenced in the Harry Potter series even take a role here, like Salazar Slytherin and the Gaunt family.

But instead of being set in the late 1900s like the original Harry Potter series, it takes place in the early 1600s. And like "Fantastic Beasts and Where to Find Them," it's set in America, not Britain.

Rowling is taking all the trivia and minutia she's had in her head and turned it into a narrative. But instead of using the same time and place as the original series, they're elsewhere. As fans, we'll be able to draw the connections between the original story and these new ones ourselves. Isn't that exciting?