Mark Duplass is a prince of mumblecore, one of the faces of an American film movement diametrically opposed to Hollywood excess and studio hierarchy. The buzz term is “low-fi” and the ethos is simple. Keep it cheap, keep it talky, don’t look like you’ve expended too much effort but maintain a highbrow-ish hipstery veneer.

Appear in too many productions with big names and six, seven or eight digit budgets and your cred in the biz of lemonade stand filmmaking naturally begins to slide. Amid the grainy surrounds of shoestring sets you run the risk of looking as inconspicuous as Jamie Oliver at a sausage sizzle or Chopper Read at a children’s party.

Director Colin Trevorrow’s breezy, smart and quirky-but-not-overtly-quirky sweetener Safety Not Guaranteed may be Duplass’ sign-off point. From here on he’s appearing in a Lawrence Kasdan pic with Dianne Keaton and Kevin Kline, a drama with Chris Pine and Michelle Pfeiffer, Kathryn Bigelow’s hunt-f0r-Osama joint…

It’s also about half a mumblecore movie, about half not, with the softest splash of SCI-FI. A kind of bridge between indie and multiplex that will play well with large crowds but has been formed with an obvious disdain for conventions. The film’s greatest pleasure is that it keeps you guessing.

Safety Not Guaranteed opens with a mopey-voiced childhood-to-adult flashback introducing us to the life of Darius (Aubrey Plaza): how she didn’t fit in as a teenager, was reclusive as a uni student, etcetera. We realise it’s a job interview and she’s “not a quality hire”.

Interning at a magazine, Darius volunteers to accompany a sleazy writer and a dorky student to a small town to track down a man who placed a classifieds ad in a newspaper asking for a partner to travel back in time with him (“safety not guaranteed”). They think it’ll make a good yarn.

When the man, Kenneth (Mark Duplass), is found, he seems a little bonkers. He swears the government are watching him while he supposedly builds his time machine, and counts down to launch date. He and Darius kick off a cautious but affectionate relationship.

Bujalski-esque conversations about chocolate milk, roommates, roast chicken, sex and relationships occasionally dip a little too far into Things White People Whinge About territory and Aubrey Plaza doesn’t quite succeed in escaping her ‘pretty young thing’ aura to nail the depth of her supposedly outside character.

However, playful plotlines, warm performances and a healthy pace quickly take hold. There are some lovely surprises in store and the last half hour or so is particularly spesh — including a delightful final sequence that perfect summarises, and adds to, the film’s semi-SCI-FI semi-mumblecore temperament.

Safety Not Guaranteed’s Australian theatrical release date: October 18, 2012.