WRITER-director Bart Layton has a bloodhound nose for a good story. In his 2012 documentary The Imposter he told the tale of a teenager from Spain who convinced a family in Texas that he was their missing child returned.

American Animals finds him with another stranger than fiction yarn, one so astonishing that even though he tells it twice, in dramatised and straight documentary forms, you are left wondering if it can possibly be true. But as the intro tells audiences: “This is not based on a true story. It is a true story.”

Layton opens with various parents sitting on sofas wondering where it all went so wrong for their teenage sons. So far, so routine. From there he rewinds to 18 months earlier and we meet art student Spencer (Barry Keoghan), a young man who reckons great lives need grand acts of daring. Spencer has a yen to do a crime and escape the punishment; specifically, steal a first edition of Audubon’s The Birds of America, estimated worth $12m, from a college library.

Spencer tells his friend Warren (Evan Peters) of his plan. Warren, being an excitable sort, seizes on the idea. Two more former high school pals are recruited, preparations are made (“how to pull off a bank heist” is Googled, and movies about robberies are watched), and before you can say, “Are these jokers for real?” we are off to the races.

At the same time as telling the story in dramatised form, Layton cuts back and forth to interviews with the real Spencer, Warren, and company. Since the locations are clearly not prison cells you might think this would be the ultimate spoiler. It is testimony to Layton’s ingenuity that it is not. If anything, your curiosity is peaked further.

The side by side stories continue to spool out, with Layton becoming more daring, putting the real people beside the actors playing them. As a narrative style it has the potential to go very wrong, but it is done with such wit and skill it adds nicely to the surreality. These are kids, after all, who cannot tell the difference between grim fact and movie fiction, who believe that robberies unfold as smoothly as in Oceans 11 or The Thomas Crown Affair, and that nothing too bad can happen to white middle class college boys.

Barry Keoghan, so impressive with fellow Irishman Colin Farrell in The Killing of a Sacred Deer, confirms his rising star status with a performance that is smart, subtle, and moving. Rivalling him is Evan Peters, who is so wired he makes Jim Carrey like demure. Co-stars Blake Jenner, the jock with the fast car, and Jared Abrahamson, playing the wannabe FBI man/accountant, more than pull their weight. Ann Dowd, aka Aunt Lydia from The Handmaid’s Tale, takes another supporting part, the librarian, and turns it into something memorable.

The plotters constantly reference movies to get their points across to each other, even giving themselves Reservoir Dogs-style code names. They could do with reading a few books: the irony of it. In time to come, given what a success Layton makes of his film, one can see other directors doing an “American Animals” with a story. It would be the ultimate compliment to an outstanding picture.

From innovation to dreary, same-old hammy horror in The Nun (15). Part of The Conjuring series of films, Corin Hardy’s picture traces the demonic nun character’s beginnings in post-war Romania.

The Conjuring films started off so well, bringing some original tricks to the familiar horror mix, but Hardy’s picture simply works its way through the cliches: creaky doors, locals believing their village is cursed, portals to hell opening, and so on. Oh, and ghostly apparitions of nuns pop up with such regularity the film starts to look like a religious version of Whac-a-Mole. Purgatory.