Starring Scoot McNairy and Whitney Able. Rated PG.

The title may seem obvious, but when it finally goes to DVD, no one will know where to file Monsters—and that’s exactly the draw of this deeply human space-invasion movie.

Brit director Gareth Edwards has a background in special effects, but in his indie feature debut, he forgoes gore for an atmospheric love story/road movie. Yes, there are monsters—huge, tentacled ones—but they almost serve as background here.

The largely ad-libbed Monsters becomes an endearing character study of jaded American photojournalist Andrew (Scoot McNairy) and Samantha (Whitney Able), the daughter of his publisher, who are both stuck in Mexico behind a quarantined area seething with angry aliens. Now Kaulder and Sam have to somehow get back to the U.S. Journeying from rickety trains to rural shacks to the top of Mayan ruins, they share their secrets: she has run away from an engagement she’s unsure about, and he has his own family demons.

The allegory is obvious, in a District 9 kind of way. Kaulder and Sam are travelling the route of illegal immigrants, and a giant border wall looks eerily familiar to the one U.S. officials are now erecting to keep Mexicans out. There’s an ongoing sense of inequality: the Americans can afford to block the giant beasties but their poorer neighbours are left to fend for themselves. That El Norte vibe mixes with a Lost in Translation one, too, in that Kaulder and Sam are strangers in a strange land.

The sense of disorientation adds to the atmosphere, as do lush shots of Central American jungles and crumbling cities. Edwards knows how to build ominous detail: there’s the constant screech of fighter jets overhead; gnarled train cars and ships are tossed onto the landscape; and warning signs are everywhere—“Zona Infecta 200 km” and “Extraterrestres: Peligro”.

Die-hard monster-movie fans may feel that the sense of dread never pays off with enough shock. But that’s exactly why Monsters feels so fresh: it’s too smart to go in the direction that 1,000 other creature features would lead you.