And indeed the alien-human romance at the heart of this story is—like the vampire-mortal relationship around which the "Twilight" saga revolves—innocent enough to be acceptable for targeted younger viewers. But other factors at play in director D.J. Caruso's adaptation of a novel by Pittacus Lore, including some hyper-violent action and vulgar language, are far less suited to that much-pursued demographic.

While our hero—a hunky interplanetary refugee who goes by the blend-into-the-background alias John Smith (Alex Pettyfer)—may have numerous problems, resembling E.T. is not one of them.

John has come to earth to prevent its colonization by the Mogadorians, a race of evil creatures (led by Kevin Durand) who took over his home planet, slaughtering the native population in the process. (You can tell they're the bad guys because they're ugly and have bad teeth.)

Though John's powers are increasing—he's number four, we learn, in a group of elite warriors bred up to defeat the Mogadorians—for the moment he's too weak to confront the enemy directly. So, in the company of his protective guardian Henri (Timothy Olyphant), he's perpetually on the run, evading his foes and hoping to make contact with the other members of his corps who have also arrived on Earth.

When John and Henri's wanderings bring them to the small Rust Belt town of Paradise, Ohio, John enrolls in the local high school where he quickly falls for comely classmate Sarah (Dianna Agron)—no Mogadorian she, to be sure.

John also befriends Sam (Callan McAuliffe), a persecuted nerd whose claim that his dad was abducted by celestial visitors makes him a target for football captain and BMOC Mark (Jake Abel).

Of course, the Mogadorians are in hot pursuit all the while, and the timely arrival of the otherwise unnamed Number Six (Teresa Palmer) sets the stage for an overheated, highly destructive—though generally bloodless—final showdown.

The few affecting moments in "I Am Number Four" are those portraying John's sense of isolation, as he unwillingly moves from place to place, and his understandable desire to rebel against the seemingly overzealous Henri, both of which parallel more mundane adolescent angst. The love story and explosive confrontations, by contrast, are strictly boilerplate.

The film contains much intense but largely gore-free combat, a few uses of profanity, a bit of vaguely scatological humor, at least a dozen instances of crude language and about half that many crass terms. The Catholic News Service classification is A-III—adults. The Motion Picture Association of America rating is PG-13—parents strongly cautioned. Some material may be inappropriate for children under 13.

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John Mulderig is on the staff of Catholic News Service.