The first half of “I Am Number Four” follows the formula for teen romance that made “Twilight” so popular. A high school girl falls for the new school hunk who just happens to have powers beyond mortal man.

In this case it’s aliens, not vampires.

The second half turns into a close-encounters-of-the-hallway kind when the high school becomes a battleground between warring alien factions.

These two genres rarely meet in such dramatic fashion. Because Director D.J. Caruso manages to blend them so well, “I Am Number Four” works.

This cinematic concoction makes it a perfect date movie.

Alex Pettyfer, who’s poised to become the latest Hollywood hunk, plays John, a teen from a distant world who is hiding on Earth. A group of bad aliens tracks John and his buddies. John is No. 4 on their hit list.

Scenes between Pettyfer and Timothy Olyphant, who plays the alien’s guardian, have both a great father-son and student-mentor feeling. Olyphant brings just enough physical and emotional intensity to keep the film from being a vapid teen-age love story.

Good thing Olyphant has so much energy and Pettyfer so much charisma, because “Glee” star Dianna Argon sucks the life out of the movie. Her character’s brooding with Argon, combined with being so soft-spoken, makes her a mousy mess.

Teresa Palmer, No. 6, is far more interesting, but she doesn’t become part of the action until the second half. When she finally gets involved, she provides enough spark to match the solid performances by Pettyfer and Olyphant.

Caruso’s skillful direction makes “I Am Number Four” work as both a romance and an action movie.