"Who can give me the derivative of X?" a high-school teacher asks early in the YA-apocalypse mashup The 5th Wave. As soon as she asks that, the lights blink off, everybody's cellphones die and jets tumble from the sky. We never hear a student respond, but here's my Official Fan Theory about this twisting, familiar story: The movie that follows is an answer to that question, the filmmakers' effort to offer the definitive derivative of X, a variable that in this case is forever in flux. Sometimes, it's The Hunger Games or Ender's Game, of course -- can't have a dystopia without teens in military jumpsuits! And sometimes it borrows from the blockbusters of yore.
The storytelling is less about character than it is about waiting for the other shoe to drop, and there's always another -- the movie is like a Payless sliding over a cliff. There are three waves of alien invasion to get through in the prologue, and then the nature of the fourth and fifth waves are minor surprises as the protagonist, Cassie (the always commanding Chloë Grace Moretz), hero's-journeys across an alien-ravaged Ohio in search of her tiny brother, who has been impressed into military service to fight "the Others." Director J Blakeson and crew quickly, strikingly establish the end-of-the-world stakes, and there's grim gravity to scenes of Moretz scrambling to escape floodwater or steeling herself to shoot a potentially dangerous stranger. But the teens talk more as the movie goes, and I'm afraid that, outside Moretz, this cast is better at being posed against Armageddon than convincingly discussing it.