At least three entertaining films are jostling for position in Australian writer-director Julius Avery’s messily propulsive debut feature, “Son of a Gun” — and if none ultimately emerges dominant, the red-blooded tussle between them is never dull to watch. Beginning as tough-minded prison drama, careering into daffily escapist caper territory and concluding somewhere in between, this London Film Festival competition entry casts Ewan McGregor brashly against type as a grizzled master thief mentoring a teenage inmate (Brenton Thwaites) through a high-stakes heist that goes inevitably off-plan. Slicker than it is smart — notwithstanding some strained chess metaphors — Avery’s film packs only moderate crossover potential, but serves as a neat calling card for bigger-ticket genre assignments. Released earlier this week Down Under, “Gun” has already secured U.S. distribution with A24.

“Things are not as you imagine,” a character intones at more than one juncture in “Son of a Gun,” as the action grows ever farther-fetched. It’s one of numerous stock lines in Avery’s busy script, and one that inadvertently alludes to the film’s own odd, shape-shifting quality: Just as viewers might think they have a handle on its genre identity, “Gun” turns out to have other ideas. To what degree Avery is driving these tonal and stylistic transitions is open to question. At best, the pic serves as a showy grab-bag of thriller varieties for which the helmer demonstrates equal aptitude; at worst, it points to a narrative attention span that hasn’t yet evolved from his award-winning short film work. (2008’s “Jerrycan” was honored at the Cannes, Berlin and Sundance festivals.)

The pic’s hard-edged opening salvo expressly recalls David Mackenzie’s recent “Starred Up” as it introduces J.R. (fast-rising star Thwaites), a 19-year-old petty criminal beginning a six-month sentence at a rough adult penitentiary in Western Australia. Very much a boy among men, J.R. — who has little of his “Dallas” namesake’s guile — is immediately vulnerable to bullying and attempted rape at the hands of older inmates, until he scores a protection deal with Lynch (McGregor, heavily bearded at the outset), a dangerous alpha-male convict hatching an intricate escape plan.

A tentative father-son bond has been established by the time J.R. is paroled and sets the plan into motion from the outside. The hitherto gritty drama, meanwhile, shifts into a more heightened action-movie mode: Complete with extravagant firearms and a hijacked helicopter, the prison break itself is a grandly outlandish setpiece worthy of the late Tony Scott. With all the principals on the outside, the film then morphs into a fairly conventional gangster drama. J.R. and Lynch’s crew fall in with Eastern European crime lord Lennox (Jacek Koman), agreeing to participate in (what else?) one last heist — a particularly complex one, targeting a literal gold mine in Kalgoorlie’s Super Pit. Friction between Lynch and Lennox is swiftly apparent; J.R. doesn’t help matters by striking romantic sparks with Tasha (Alicia Vikander), a wily member of Lennox’s jealously guarded coterie of women.

Once the high-octane mine job is completed, the situation goes awry in ways that might be termed predictably unpredictable. The usual litany of switchbacks and double-crosses ensues, keeping the film diverting enough — though in terms of structural intricacy, it hardly lives up to the script’s early symbolic invocation of chess’s famed Benoni Defense. (As is so often the case in films featuring any chess-related subtext, it exists primarily to give one character the satisfaction of uttering “checkmate” as a hard-boiled punchline.) A heavily plotted final act aims for the best of all possible worlds, balancing near-fantastical genre mechanics, noirish romantic resolution and episodes of unvarnished violence that appear slotted in from a more severe school of non-Hollywood crime drama.

Thwaites, recently seen in “Maleficent” and “The Giver,” makes a suitably keen-eyed, clean-scrubbed lead, retaining a kind of porous naivete even as the character gets his blood up. Vikander is a curious fit for a familiar femme fatale (or semi-fatale, at least) role that doesn’t play to her subtly inquisitive strengths as a performer; still, she does enough to make one wish this testosterone-dominated film were more than passingly interested in her, or women in general. With Lynch neither a pure antagonist nor the keeper of the film’s perspective, McGregor’s casting is more purposefully counter-intuitive. Exhibiting some of his own tattoos and putting a guttural Irish spin on his Scots brogue, the star effectively deploys his everyman charisma on a character who occupies far scuzzier moral ground than he’s used to playing.

Technically, the film adeptly rolls with the script’s highly varied punches, with Nigel Bluck’s lensing alternating between intimate, verite-style desaturation and the kind of florid orange-and-teal action panoramas chiefly associated with high-concept Hollywood. More tonally committed is the anxious, low-humming score by Jed Kurzel (“The Snowtown Murders”), which merges with the ambient-buzzsaw sound design in a comparable manner to the integrated sonic textures of fellow Australian David Michod’s first two features. That’s unlikely to be the last time Avery and Michod are mentioned in the same short breath.

Film Review: ‘Son of a Gun’

Reviewed at De Lane Lea preview theater, London, Sept. 24, 2014. (In London Film Festival — competing.) Running time: <strong>108 MIN.</strong>

  • Production: (Australia) A Screen Australia, Screen West, Lottery West, Screen NSW presentation of a Southern Light Films production in association with Media House Capital, Daydream Prods., Hopscotch, Entertainment One, Bridle Path Films, WBMC. (International sales: Altitude Film Sales, London.) Produced by Timothy White. Executive producers, Aaron L. Gilbert, Clayton Smith, James Dean, John Collee, Michael Spiccia, Aidan O'Bryan, Richard East, Bryce Menzies. Co-producer, Janelle Landers. Co-executive producers, Margot Hand, Patrick Murray.
  • Crew: Directed, written by Julius Avery. Camera (color, widescreen), Nigel Bluck; editor, Jack Hutchings; music, Jed Kurzel; music supervisor, Jen Taunton; production designer, Fiona Crombie; art director, Sophie Nash; set decorator, Nicki Gardiner; costume designer, Terri Lamera; sound, Trevor Hope; supervising sound editors, William Ward, Andrew Plain; re-recording mixers, Robert MacKenzie, Sam Hayward; visual effects supervisor, Nicholas Ponzoni; visual effects, Blackbird Studios; stunt coordinator, Chris Anderson; line producer, Catherine Bishop; assistant director, Chris Webb; second unit director, Michael Spiccia; second unit camera, Jac Fitzgerald; casting, Nikki Barrett.
  • With: Brenton Thwaites, Ewan McGregor, Alicia Vikander, Jacek Koman, Matt Nable, Tom Budge.