History is marked by ill-advised attempts at extending movie franchises. When a studio with a hot (or moderately successful) property runs out of stories it often scratches around for potential spin-offs, hoping to monetise anything that can loosely be associated with that once popular thing. When Peter Jackson was ordered to squeeze three movies out of wafer thin Lord of the Rings prequel, The Hobbit, moviegoers cried foul, sensing a dilution of material. But one wonders what those genre fans make of Fantastic Beasts and Where to Find Them, an original script from J.K. Rowling developed from a textbook she quickly scribbled for charity. In other words, here’s a Harry Potter spin-off spun from a concept rather than a story. The challenge for those adapting Rowling’s novels was to condense them into filmable chunks. The challenge Rowling’s set herself is to build a movie from scratch; a frightening prospect as no one can vouchsafe her screenwriting credentials.

So the big question for Potterheads is whether Rowling’s magic works in any medium or if she should stick to the written word. On the evidence of David Yates’s movie, she should be more protective of her intellectual property and resist vanity commissions. Fantastic Beasts is an inoffensive fantasy, but it lacks the three constituent elements that one suspects powered Potter’s popularity – the mystique and eccentricity associated with its British setting, vivid characters in the Dickensian tradition, and a solid proxy for the consumer.

Rowling attempts to compensate for the first by setting the movie in 1920’s New York, once again blending the fantastical with the historic. But the backdrop, though well-realised, has far less personality, not least because it often feels synthetic due to the movie’s over reliance on CG. The characters are weak and largely anonymous. Eddie Redmayne’s a likable hero – sweet natured, suitably kooky, but he’s a small peg on which to hang a new franchise. Harry Potter was a non-entity too of course, especially in the form of Daniel Radcliffe, but he was surrounded by big personalities. Beasts offers a drippy Katherine Waterston and a dolly bird in the shape of Alison Studol – hair and teeth.

But it’s the movie’s audience proxy, Dan Fogler’s factory worker and would-be baker, that tells the story. He’s a flat and lifeless character, who has little more to do than look amazed and ask questions, whose lack of guile and wit, saddles the film with a nondescript page turner. As Harry Potter learned who he was, we learned of his world. Fantastic Beasts attaches us to a boring story tourist who follows a drip around town, catching special effects. This does allow for an unintentionally hilarious scene in which Redmayne is almost violated by an ovulating magical rhino, but that’s scant compensation for how beige the rest of the film is.

Rowling has a go at alternative world building, or rather expansion, and tries to make it relevant (perhaps interesting) by exploring the American context. Consequently, we get an allegory for racial segregation, with the US of the Potter Universe a place where the yanks treat non-magical folk like a sub-species, with mixed marriage and social contact strictly forbidden. Was is it about the American character, you say, that inspires even their magical population to discriminate? Still, neither this, nor other spin-offs from the American setting – the New Salem Anti-Witch movement for example, stoke much interest. There’s just not quite enough story to make this feel like a curtain raiser to exciting new series, so news that there’s four more films to come makes the heart sink rather than soar.

That sense of it all being a bit rote and taped together using blockbuster (and reused) elements – special children, hidden villains, monster-made citywide destruction, is compounded by Yates’s direction, which though employing a more colourful palate than his Potter chapters, is subordinate to pre-visualised CG setpieces that invest the film with a sheen of inorganic artifice. It’ll do as dessert for Potterheads then, but if Rowling wants to avoid doing damage to her cash cow, she’ll need to find better characters and a bigger story to occupy what could otherwise by four long, event free sequels.