Time-travel stories are always tricky. As a viewer, you have to accept paradoxes and twisting strands of plot, and writer-director Rian Johnson’s Looper — the fall film I looked forward to the way some people anticipated The Master — will not hold your hand on this matter. The explanation is quick and to the point: In the future, time travel will be invented, then outlawed, then used by outlaws. The future mob hires loopers, men (and only men, apparently) who assassinate victims who have been sent back in time to be killed. Joe (Joseph Gordon-Levitt) offs his targets in a cornfield. Hooded and bound, they appear on a sheet of plastic. He shoots them, collects his bounty (in silver bars strapped to each victim’s back), disposes of the bodies, and heads out on the town.

The particularly ugly thing about being a looper is that at some point, you have to off yourself. When a looper finds gold bars strapped to his victim’s chest, he know the powers that be have decided that his time is up. The job is done, and the looper has 30 years of nice retirement until he kills himself (in a complicated way). It’s nasty, but what they do to you if you let your old self go is stomach-turningly vile, as Joe’s friend Seth (Paul Dano) learns.

What happens when your old self, sent back for your disposal, breaks free and goes on a rampage is something entirely different. When old Joe (Bruce Willis) appears in the cornfield, he’s unbound and bare-headed, and the shock of recognition gives old Joe all the time he needs to disarm young Joe and take off.

Old Joe has a mission, a yen for vengeance that he hopes will change the future, where a crime boss called the Rainmaker is killing off loopers left and right. As his elder self hunts down the future Rainmaker, hoping to stop this violence before it can happen, young Joe takes refuge on a farm belonging to Sarah (Emily Blunt), a prickly single mother with a talented young son, Cid (Pierce Gagnon). The farm is old-fashioned and rich with golden light; Cid’s childish clutter stands in extra-stark contrast with the city’s glassy lines. Sarah’s place is a home, whereas the city, as Joe experiences it, is an indulgent, withering hell, a place of lens-flare-dappled extremes in which the middle class seems to have disappeared. (It’s not hard to see Johnson extrapolating on the fraught present, but he doesn’t harp on the parallels; there are plenty of other ideas for him to get to in Looper’s zippy plot.)

Johnson’s storytelling, as always (Brick, The Brothers Bloom), runs deeper than his high-concept plots might suggest. Gordon-Levitt and Bruce Willis play off each other with surprisingly well-matched intensity, and as the film zips through a montage spanning the years one man spends aging into the other, there’s fodder for a dozen spinoffs. Can you age into a person your current self wouldn’t recognize? What do you do when faced with a self whose goals and desires are so utterly contrary to you own? What causes such a rift?

Looper embraces the paradox that’s required for the two-Joes story to even happen, knotting improbability, vengeance and the notion of choice into a taut, sleek, imperfect but intelligent action movie. The story is the thing, but you also have to let go of any need to neatly line up the narrative pieces; trust the tale. Where Looper slips a little is in its slightly heavy-handed musings on nature and nurture and what makes us the people we grow up to be. For all the complicated thematic quandaries the time-travel plot provides — Can you make decisions for yourself 30 years in advance? Can time travel be used for good, or only to create the illusion of choice? Does one decision change everything, or just one thing? — the film’s finale hinges on a peculiar combination of sacrifice and oversimplification. It’s still a fascinating trip, but it ends with a bang and a whimper — which is rather fitting, given the inherent paradoxes. 

LOOPER: Written and directed by Rian Johnson. Cinematography, Steve Yedlin. Editor, Bob Ducsay. Music, Nathan Johnson. Starring Joseph Gordon-Levitt, Bruce Willis, Emily Blunt, Paul Dano, Piper Perabo and Jeff Daniels. Tri-Star Pictures, 2012. R. 118 minutes. Three and a half stars