Forget everything you know (or your future self knows) about time travel.

“Looper,” writer and director Rian Johnson (“Brick”)’s new film, asks the audience to invest brainpower in its twisted plot, and he makes sure the investment pays dividends.

At the beginning of the movie, viewers are introduced to Joe (Joseph Gordon-Levitt, “The Dark Knight Rises”), a twenty-something specialized assassin called a looper. Loopers exist in a time about 30 years in the future, when time travel has been invented and immediately outlawed. Mobsters use it to send enemies back to the past, where Joe waits to blast them with a shotgun.

The body gets disposed after the blast, and no record of the person exists.

The mob doesn’t like to leave loose ends. Because of this, the mob sends loopers the future version of themselves to kill when it is done with them. The loopers know they are retired when this happens, and they have 30 years to live before getting sent back to be killed by a younger version of themselves. This process is known as “closing the loop.”

Joe’s loop has just been closed in the film, but it’s not that easy.

Joe’s future self (Bruce Willis, “Die Hard”) fights back, and several secrets about the mob leaders’ true nature are revealed as younger Joe hunts down older Joe.

The magnificent thing about “Looper” is how tight-scripted it feels.

The feeling is similar to 2010’s “Inception,” which felt tight through its discussion of dream. In both, filmmakers deal with time travel, a plot device often associated with plot holes. However, the two films are fully fleshed out. Johnson took careful consideration while writing this script.

The prosthetics used to make Gordon-Levitt look more like Willis are stunning. Gordon-Levitt also mastered Willis’ mannerisms right down to his eye movements and speech style. This is true dedication on the young actor’s part.

The supporting cast, however, is a little weaker than the leading roles.

Emily Blunt (“The Five-Year Engagement”) plays a woman whom younger Joe holds up with after the mob begins hunting him for his failure. She plays a crucial role to the plot, but she seems to react to other characters rather than acting herself. Jeff Daniels (TV’s “The Newsroom”) gets a few funny moments as a mob boss, but his part is cut short.

Other critics compare “Looper” to 2006’s “Children of Men,” and that is right on target. Joe exists in a world where violence runs rampant, and average citizens carry shotguns to protect themselves from vagrants.

Willis commits several unspeakable crimes once he is unleashed in the present, which — all spoilers aside — are sure to make viewers’ jaws drop.

As the film progresses, though, it loses some originality and takes plotlines from other famous time travel movies. This becomes a little too absurd, but it remains only a minor complaint since the film keeps the borrowed plot fresh and certainly never gets boring.

As far as this year goes, it doesn’t get much better than “Looper.” The writing, pacing and acting are all solid. If the second half were as good as the first, I’d give it 5 stars. Nevertheless, the movie is still one of the best sci-fi films in a long time.

1hr 58min? – ?Rated R? – ?Action?