‘The 5th Wave’ follows standard YA playbook

One major reason that young-adult fiction is so alluring — when done well — is that it gives youngsters such a fulfilling scenario of independence from those older adults in their lives who always think they’re smarter and stronger. That scenario is front and center in “The 5th Wave,” where every adult is either evil, inhuman (literally), or nice but helpless. It’s truly up to the young — make that the young, buff and good-looking — to save humanity.

But if this movie, starring Chloe Grace Moretz, performs its appointed task with efficiency, it does little more.

Yes, the winsome Moretz is a fine, if one-note, reluctant heroine (the film’s based on Rick Yancey’s best-selling novel, and directed by J Blakeson). And she’s surrounded by more than one appealing young man (the YA action-film rulebook seems to dictate at least two, so we can have a triangle.) But the script has more than a few lines that should have been sent directly to rewrite, and there’s a nagging feeling throughout that we’ve sorta seen it all before.

Not that this will deter fans of Yancey’s book, which is the beginning of a trilogy, meaning we’re sure to see more of Moretz’s Cassie in years to come. She is, when we first meet her, a pretty perfect Ohio high-schooler. Yes, she goes to a party and drinks beer and crushes on a cute football player named Ben. But then she goes home early and sings her little brother Sam to sleep.

The next day, life changes forever. A giant alien craft appears in the sky. For days, the Others, as the aliens are known, don’t make a move. Then come the four waves. First all power and technology is knocked out; planes and cars crash. Then giant tsunamis are unleashed, killing billions. Then there’s crippling disease, transmitted by birds and killing countless more. The fourth wave brings attackers to Earth in unexpected form, all building up to the climactic fifth wave.

Meanwhile, Cassie, her brother and father have left home for a refugee camp. When the U.S. Army’s Col. Vosch (Liev Schreiber) orders youngsters onto a school bus to a military base, the family reluctantly agrees.

But Cassie and Sam are separated when Cassie runs back for Sam’s stuffed toy. Cassie is forced to follow on foot, a journey of many miles. On the way, she reluctantly kills a man, nearly gets killed herself by shooting attackers, and wakes up, wounded, in the house of a very cute guy named Evan (Alex Roe).

The final act of the film sees Cassie and football player Ben (played by Nick Robinson) uniting to try to repel the evil forces from Earth.