Forget time travel. In the future anything can happen, because Joseph Gordon-Levitt may end up looking like Bruce Willis.

In science fiction premise is everything; the more plucky and loopier, the better. Ergo: Rian Johnson’s Looper, an absorbing futuristic thriller of mob hit-men snuffing people from the future, in our would-be future — Or something close to the effect.

Johnson’s sci-fi fable, where he shoos-away the mechanics of time-travel, is a perfect short-story out of pulp anthology magazines: Our future, 2044, has yet to discover time-travel, which is already banned in its future, 2074, where the law is quick to nab murderers. So whenever future-mob needs someone hit, they transport the victim, bound and face-covered, 30 years back where a specialized mob-deputy — dubbed “Looper” — takes him out. Loopers, and there are a handful, are employed by Abe (Jeff Daniels), a future-traveller sent to manage these hits.

Like any work contracted by syndicated criminals, the pay-scale is ludicrously lucrative (Loopers are paid in solid silver bars, strapped to their hit’s back). Their exit strategy is simpler still; their contract ends when they shoot their future-self sent back to close “their” loop.

Now imagine this: Joseph Gordon-Levitt (always engaging), with his lip-thinned and nose prosthetically-lifted, is a young, aimless, junkie Looper called Joe with a great retirement plan: he plans to relocate to France, when he closes his loop.

One “routine” day at his job — after a riveting unvaried-cycle self-centering on Joe’s colorless, and tirelessly “looping”, routine — Bruce Willis pops into frame, gag-free, beats him up and runs loose with an ulterior agenda (he has a future-wife, played by Xu Qing, he wants to live happy with).

When younger Joe wakes up, he finds a simple message from his future self: Runaway to China.

The younger version, horrified by the implications of time-space conundrums, and more-so of the mob’s doctrine on botch-ups — body parts are mangled-off, which automatically disappear on their present-self, as we see in one panic-provoking scene — he goes on the run to gun-down his future-self.

But before the body-count rumbles down, there’s a mute little scene between Gordon-Levitt and Willis in a diner (past-future selves have an ingenious way of communicating we’re shown). Willis, sparkling with anticipation of edging out a punch-line, and visible hint of madness-seen matureness, wants to take down the mob, and a mysterious evil telepathic who is closing loops in the future; Gordon-Levitt just wants Willis to roll-over and play dead — literally.

Looper, fiercely original half-way, notches down and shifts themes to Terminator-like setting when Sara (Emily Blunt), a single-handed farmer and her telekinetic kid Cid (Pierce Gagnon), are included via a initially planted MacGuffin.

Loopers’ uncomplicated, straight-forwardness is disarming, because it maintains flight an inch or two below the show-bizzy radar of big, bombastic blockbusters. With just a few minor air-bumps that make it blink-up into sensors, Johnson has created a hard-wearing, semi-burly sci-fi whose biggest suspension of belief is its insistence that Gordon-Levitt will mature into Willis 30 years from now.