Darius Britt, the heroine of the stripped-down time travel comedy Safety Not Guaranteed, can barely remember a time where she was hopeful or optimistic. Nowadays, she says, "I just expect the worst." Darius is played by Aubrey Plaza, and it is not exactly casting against type; Plaza co-stars on Parks and Recreation, where her delightfully bone-dry line readings and biting deadpan never fail to beguile. Safety is her first starring role (she played supporting roles in Funny People and Scott Pilgrim), and it may as well be accompanied by fanfares. She's got a terrific screen presence, and the camera simply loves her. She also picks her project well--this modest effort is utterly enchanting.

Darius is an unloved intern at a glossy Seattle magazine who volunteers to investigate a peculiar classified ad, seeking out a "partner" to travel through time. Smug writer Jeff (Jake M. Johnson) brings interns Darius and Arnau (Karan Soni) to the coastal town from whence the ad originated; Darius does some amateur sleuthing and lands on Kenneth Calloway (prolific indie filmmaker Mark Duplass). Darius is the most promising "undercover" agent of the bunch, so she offers herself up to accompany Kenneth on his mission.

It's pretty clear, from their first meeting, that he's met his match--the scene is Plaza's comic high point, vamping her way through the tough-girl charade ("Well, there's no sense in nonsense, especially when the heat's hot"). As she spends more time with Kenneth, embarking on a "training" regimen for their "mission" (target practice, hand-to-hand-combat, long-distance running), she's not quite sure what to make of this guy, and neither are we. Clad in a jean jacket and driving a sports car, both of which appear to date from the mid-'80s, he comes off at first like a broad, survivalist, paranoid caricature. But there's a specificity to the character, to his syntax choices and manner of carrying himself. I've known a couple of guys like this, and I get the feeling Duplass has too.

Meanwhile, Jeff (a writer with an apparent aversion to actually writing) has taken the opportunity of the trip to track down and reconnect with a girl he dated as a teenager. Early on, his plotline seems disconnected, almost a distraction, until its thematic link becomes clear: he's looking to travel through time as well, albeit in a manner less literal and (presumably) more easily achieved.

For most of its running time, Safety Not Guaranteed hums along on its charm and quirk. Derek Connolly's script is composed of short, punchy scenes, and Colin Trevorrow's direction is a model of efficiency; there are moments where he gets a laugh with a well-timed cut. His triumph, though, is in his smooth manipulation of the picture's tonal variations. He shifts into contemplative pathos and genuine wonder in the third act with such skill that it's almost a sneak attack--you're surprised by how absorbed you've become in this nutty little picture.

I'll confess to being left a little agog by the film's ending, which has to do about twelve difficult things at once, and does them all without bobbling a single one of them. There's a charge in watching a filmmaker take the kind of chances Trevorrow does, and pull it off; this viewer exited the screening with a big grin and a couple of leftover goosebumps. Safety Not Guaranteed is a genuine original.

Jason lives in New York. He holds an MA in Cultural Reporting and Criticism from NYU.