“The Host” opens Friday at Point, Eastgate and Star Cinemas. PG-13, 2:05, One and a half out of four stars.

Character actors ought to get a special rate when they’re required to make complete nonsense sound convincing in a movie. Even the silliest movie calls in a Stanley Tucci (“Jack the Giant Slayer” and the upcoming “Percy Jackson: Sea of Monsters”) or a Tim Robbins (“Green Lantern”) to try and peddle the ridiculous.

William Hurt ought to get triple the going rate for making “The Host” a little better than it ought to be, right from the prologue, in which we see a shot of Earth, as Hurt says, “The world had never been more perfect. But it wasn’t our world anymore.” Ka-ching!

The world, in the silly and drippy sci-fi romance based on Stephenie (“Twilight”) Meyer’s novel, is now largely controlled by aliens, little thingies that look like fibre-optic caterpillars. They burrow into a human’s body and control them; outwardly, the only sign a human has been “occupied” is that his eyes glow like the power button on my Dell, and he forgets how to use contractions.

Meyer’s books have always had something of a conservative streak lurking beneath their supernatural mash sessions (what’s “Twilight” but not an extended pro-abstinence metaphor?), and it feels a little more overt in “The Host.” The aliens’ idea of a perfect society looks a lot like a latte-sipping liberal’s, with no war, the environment “healed” and a suspicious amount of Volvos and VW beetles on the road. With its tale of “real’ humans fighting against a collective that thinks it knows best, “The Host” overlaps with those “one world order’ Christian thrillers that Kirk Cameron keeps starring in.

Fighting these aliens, who favor white suits and shiny cars in the tradition of sci-fi aliens for generations of bad movies, is a ragtag human resistance. Melanie (Saoirse Ronan) is one of the still-humans; she’s captured by the aliens and has a squiggly new roommate implanted into her brain.

But this alien (named Wanderer, lately shortened to Wanda) hadn’t reckoned on Melanie’s force of will, and this turns into an internal tug of war, with Melanie’s angry thoughts and retorts to Wanda heard in voiceover. This might have worked in the novel, where dialogue can overlap seamlessly, but it’s a terrible decision for a movie, with the nagging Melanie coming across like the Great Gazoo to Wanda’s Fred Flintstone (“Don’t steal my boyfriend, dum-dum!”)

Melanie convinces Wanda to escape the aliens, and together Melanie/Wanda head to the resistance hideout in the desert, run by Hurt in full old-coot mode. (I mean, his name’s Uncle Jeb, he can’t help but be coot-ish.) The humans see Wanda’s glowing eyes and peg her as an alien, but eventually accept her into the camp because . . . there’s no movie otherwise? I honestly couldn’t figure that part out, or why Melanie insists that Wanda not tell the humans that she’s in there too.

The trailers show action-packed car chases and gunfights, but that’s just one extraneous scene. Most of “The Host” is a long, leisurely-paced hang in the resistance hang, as the humans learn to like and trust Wanda, and together Wanda and Melanie try and figure out how to reverse the alien infestation. Melanie reconnects with her old boyfriend, while Wanda starts flirting with another boy, which, since they’re in the same body, should make double-dating super awkward. Oh, and a bunch of aliens in shiny cars and helicopters, led by Diane Kruger, tool around the desert looking for them without much success. I guess nobody told the aliens how the satellites worked.

I like Ronan, and I feel a little bad that the movie requires to do so much frenzied arguing iwth herself, eliciting titters from the audience. Hurt is always fun to watch, and Niccol does have a distinctive visual style, best shown in the surreal image of a golden field of wheat growing  deep inside a cave.

But the source material is just too thin and mushy, with Meyer more interested in a tired love triangle than the narrative possibilities of the world she created. The aliens are kind of interesting — they’re not evil, and genuinely think they’re doing the planet a favor by occupying it. But the film is more interested in attractive teens getting all moony-eyed with each other (even if some of those moony eyes are glowing) and trying to start the inevitable franchise. Good luck with that; “The Host” is a movie about a girl with two minds, and it barely has one.