Meet the new mutants, same as the old mutants … or sort of. This is an X-Men spin-off, based on the characters by Marvel Comics artists Chris Claremont and Bob McLeod, and they are younger than the hirsute and clawed figures of Magneto, Wolverine and the rest. The film interestingly presents an origin story in less conventional terms than usual. It brings a kind of YA horror dimension to the mutant mythology – or perhaps it just amplifies the YA horror that was always implied but less apparent in stories about infant superheroism and callow destiny. Director and co-writer Josh Boone is best known for The Fault in Our Stars and is perhaps interested in the idea that superpowers are the result of some awful cosmological defect.

This new graduating class is led by Dani Moonstar, a Cheyenne mutant played by the Native American actor Blu Hunt. When Dani survives a supernatural storm that wipes out her family on their reservation, she awakens handcuffed to her bed in some secure medical facility, far from home. The doctor in charge is Cecilia Reyes (a coolly severe Alice Braga) and there appear to be no other staff. She introduces Dani to the other slouchingly resentful student-patients in various 12-step-style encounter sessions, each of whom is nursing a superpower as symptom of some awful secret in their past.

Anya Taylor-Joy plays a Russian with the outrageous name of Illyana Rasputin (why not just knock off the “Ras” and have done with it?) who whispers conspiratorially to the hand puppet she has carried with her since childhood. Maisie Williams is Rahne, from Scotland, who has been traumatised by religious elders with the sort of nasty vengeful beliefs I haven’t seen since Lars von Trier’s Breaking the Waves. Bobby, played by Henry Zaga, is a handsome, wealthy and buff young Brazilian guy whose sexual history isn’t perhaps quite the parade of successes that he likes to imply, and Charlie Heaton plays Sam, a boy from a mining town in Kentucky also scarred by a calamitous family event.

All five are so institutionalised that, despite their badass attitudes, they have all but forgotten to ask on what authority they are kept here. Are they under arrest? Have they been sectioned? Are they being protected from someone? Dr Reyes isn’t saying. Slowly the quintet begin to come to terms with the idea that their powers have origins they are being encouraged to suppress, not examine, and everything they are experiencing is a result of a psychic wound. And they must ask the question: are they the good guys or the bad guys?

Eventually, perhaps inevitably, The New Mutants builds to the gigantic CGI battle that is a third-act imperative for everything like this, but not before we get some interestingly downbeat One Flew Over the Cuckoo’s Nest-style confrontations. This film is no masterpiece, but the franchise has mutated, just a little.

• The New Mutants is released in UK cinemas on 4 September.