How do you turn a 128 page textbook into five blockbuster films? If anyone knows, it is JK Rowling, the author who transformed a 500-copy print first run into one of the top 10 bestselling books of all time. With her boy wizard finally reaching adulthood in her play Harry Potter and the Cursed Child, Rowling has announced Harry is “done now”, but she seems up for mining her own bountiful world for further inspiration. So she has written her first screenplay: Fantastic Beasts and Where to Find Them, which, as you will know from any surface that can fit an ad on, is out in cinemas now. It is the first of a planned five-film franchise to be written by Rowling, which follows “magizoologist” Newton “Newt” Artemis Fido Scamander as he adventures around the world studying and capturing fantastical animals (think of him as a magic Charles Darwin).

Rowling makes clear from the outset that Newt is not Harry 2.0. While the scale of her world was previously constrained by Potter departing to Scotland every year to get an education, with Newt, a thirtysomething public servant, she has access to a far wider canvas. We first meet him in 1920s New York – almost 60 years before Harry is even born – where he is attempting to return one of his animals to its native habitat in Arizona when shenanigans ensue and a bunch of beasts escape from their home in his Mary Poppins-style briefcase.

Comparing the first Harry Potter film (2001’s Harry Potter and the Philosopher’s Stone) with the last (2011’s Harry Potter and the Deathly Hallows Part Two) is somewhat akin to comparing Bambi with Reservoir Dogs. The first two films, Philosopher’s Stone and The Chamber of Secrets were directed by king-of-the-kids-film Chris Columbus, and were packed full of twinkly-eyed charm. Mexican filmmaker Alfonso Cuarón directed the third, The Prisoner of Azkaban, and introduced a much darker, Tim Burton-esque aesthetic. Harry Potter’s fourth outing, The Goblet of Fire, contained the franchise’s first onscreen death, starting a trend that escalated with every following film; by the two-parter finale, Hogwarts teachers are laying out bodies in the school hall.

Darkness does not come in the form of death in Fantastic Beasts. For her new world, Rowling has included more familiar troubles; Newt’s world is closer to our own than Harry’s was. As the author has demonstrated so often on Twitter, she’s political and not afraid to show it. There are many references to the positives of equality and embracing differences. Allusions to the history of US segregation pop up: magical and non-magical people are not allowed to marry – a rule that the Englishman Newt frowns upon – and house elves are only seen in service roles, as wand shiners, and so on. It is clear this world is our world, albeit with a twist; Newt even served in the first world war (with dragons on the eastern front). Rowling has said the film series will end in 1945, with the second world war coinciding with the defeat of the wizard Grindelwald – who Potter readers will remember has troubling ideas about wizarding superiority over non-magical humans. There is much here that will sail over the heads of little ones who are there for the animals and tie-in toys that will inevitably come – really, this is a film for the twentysomethings who might be tempted by the Moleskine journals (there’s a line of those already).

While the film may be new, the tiny book it is based on has a longer history. A little dictionary of animals called Fantastic Beasts and Where to Find Them, written by Scamander in 1927 and by then in its 52nd edition, was read by Potter at school during his first year. When Bloomsbury published the fictional textbook in 2001 it was easy – and right – to be sceptical. But Fantastic Beasts was something more than a display of publishing cynicism. Much thought and creativity went into it, with ink notes in the margins doodled by Harry and Ron during a boring class. Strange illustrations of the creatures also appeared alongside their descriptions, which were as outlandish as their Roald Dahl-esque names – flobberworms, kneazles, puffskeins, murtlaps. There was a foreword from the wizard Albus Dumbledore about Newt, describing the oddball as one of his favourite students at Hogwarts. And more than 80% of every copy sold went to charity: in 15 years sales of Fantastic Beasts and its sister-textbook Quidditch Through the Ages have made over £20m for Comic Relief.

Fantastic Beasts is currently out of print with copies of the £4.99 book now selling for upwards of £30 online. A new hardback edition, which will be almost three times as expensive as the old paperback at £12.99, is scheduled for March 2017. But what we do have is Rowling’s Fantastic Beasts and Where to Find Them: The Original Screenplay (Little, Brown) published last week. It is handsome and embossed, but reading actions and transitions is dry work. There are no extra scenes – despite director David Yates confirming they were filmed and promised for the DVD version – or Easter eggs for fans who have already paid to see the film (possibly multiple times). There is nothing included from its diminutive and more interesting literary source, with the only extras being a glossary of film terms and a thank you letter from Rowling.

It is a shame the published screenplay is so empty when the film is so rich, in imagination and detail. But this is a rare miss for Rowling’s wizarding world: of all the Potter merchandise, video games and theme parks, the books remain a lucrative part of the brand with sales of around $8.2bn (£6.6bn), second only to the $11.6bn (£9.3bn) made by the films. There is something wonderful about a franchise that gains so much of its cashflow from book sales. Even the more questionable publications, such as the “adult” editions of the books (read: different covers), the Pottermore ebooks pieced together from content already online, or the playscript of Harry Potter and the Cursed Child, published as a book in July, have their worth. The play, for example is currently showing in a single theatre in central London, so its book form allowed global fans to consume the plot long before they can see it.

There is no similarly compelling reason for anyone to purchase the new Fantastic Beasts screenplay, but nostalgia is a lucrative emotion. As part of the generation that might name their firstborns Hermione or Harry, and then be willing sell off said firstborn for the prospect of an eighth Potter tale, it can be hard to remain discerning. But I’ll end on some sacrilegious advice: skip the book, watch the film.