Imagine an earth in the near future where there is no more hunger, no more war, and everyone is at peace. Life is being lived just as it always has, but without the need for money or government. People are kind, helpful, and trusting to a fault, working within jobs because they want to, not because they have to. It sounds like a dream come true, at least in concept, but there's also a sizable downside: nearly all human bodies have been taken over by an alien species that has invaded our planet and claimed it as their own. A handsome adaptation of the best-selling novel by "Twilight" writer Stephenie Meyer, "The Host" is an original sci-fi vision from writer-director Andrew Niccol (2011's "In Time"), one that takes chances, falls on its face a time or two, and otherwise works as well as it does because of how brazenly different it dares to be.

In this utopian world of tomorrow, the few humans who have escaped the initial waves of colonization are on the run. Such is the case with Melanie Stryder (Saoirse Ronan), a defiant, strong-willed teenage girl taking care of her younger brother Jamie (Chandler Canterbury) until an attempted escape out a window nearly kills her. Overtaken by an alien named Wanderer, Melanie talks to the new occupant sharing her body and eventually convinces her to go on the run to find her brother. With The Seeker (Diane Kruger) hot on their trail, Wanderer eventually finds Jamie and is spared her life by Melanie's sympathetic Uncle Jeb (William Hurt), who brings her into their community's cave hideout. As Melanie struggles to find a way to free herself and Wanderer begins to feel for this girl whose body she's stolen, the two of them are torn by their interest in two different guys: Melanie's now-bitter boyfriend Ian (Jake Abel), and Jared (Max Irons), who has fallen for Wanderer, nicknamed Wanda.

"The Host" smoothly sets up the time, place and fantastical circumstances of its story very quickly and with minimal cheesiness, then dives into its even more curious, but necessary, storytelling conceit: that much of the interpersonal drama takes place between Wanderer and Melanie, the two of them at war over the same body and their own free will via Wanderer's spoken dialogue and Melanie's voiceover. The inner monologues from Melanie probably do work a little better in written form than when they are actualized onscreen, but save for the occasional stilted line—"I hate you. If only I could hurt you..."—it is easy to get used to and has a certain charm about it. Surely, it aids immensely in the viewer never forgetting that there are two separate entities coexisting in the film's heroine, each one with her own thoughts, ideas, and fears.

Expressive and identifiable, Saoirse Ronan (2011's "Hanna") is ideally cast in a dual role that, one can imagine, must have been doubly difficult since it involves no special effects trickery. Instead, everything must occur in a singular body, and Ronan retains a feisty dignity and resolve as Melanie, and a wizened empathy and vague otherworldliness as the thousand-plus-year-old Wanderer. No matter who she's playing, she wins over the audience. If there is a disappointment in what Stephenie Meyer has wrought, it is her insistence, once again, in having her lead female protagonist fulfilled by a significant other. While doing nothing for modern feminism, the two guys she pits Melanie/Wanderer against are rendered bland and blander. Jake Abel (2011's "I Am Number Four"), as Ian, and Max Irons (2011's "Red Riding Hood"), as Jared, are undercooked in the development department, and while the notion of Ian in love with Melanie and Jared in love with Wanda is pleasingly quirky—that's something we've never seen before—both romances derive out of convention rather than natural connection and chemistry. As the lead Seeker out to capture Wanderer and find the humans she has gone to protect, Diane Kruger (2011's "Unknown") makes for a coldly beautiful adversary, while William Hurt (2010's "Robin Hood") gives a calm, grizzled warmth to Uncle Jeb.

Though the production design and art direction within the living quarters of the cave where Wanderer unites with Melanie's brother, relatives, and surviving human stragglers is impressive, complete with an underground wheat field and a deadly volcanic waterfall, "The Host" threatens to catch a case of cabin fever in the second half. This nagging claustrophobia, however, lessens once the characters must journey outside, first to find medicine for an injured Jamie, and then for crucial late reasons that will remain undisclosed. The opening-up of the scope of this skewed world that is like the earth we know, only not—when Wanderer stops an elderly driver on the street and asks if she can take his car, he gladly gets out and lets her have it—is fascinating to behold and arguably could have been more deeply explored. All the same, "The Host" goes about proudly playing to its own drummer, with director Andrew Niccol bringing a slick, heartfelt, wondrous sheen to a project that could have easily turned more egregiously ridiculous and cornball in lesser hands. A story of sacrifice, redemption, and little, squiggly, glowing life forms, it's all still kinda-sorta B-grade hogwash, but it's eloquent, B-grade hogwash. Sometimes, in this genre, that's more than enough.