Max Irons and Jake Abel are chasing each other up and down a hallway at the Ritz-Carlton in Philadelphia while Stephenie Meyer looks on with a maternal smile.

They’re blowing off steam after a solid block of media appearances to promote their new film, “The Host,” an adaptation of Meyer’s 2008 best-seller. The film, Meyer’s follow-up to the blockbuster “Twilight” series, opens Friday.

The actors – either of whom could give Robert Pattinson a run for his money as a movie heartthrob – form two sides of a very peculiar love triangle (or perhaps more accurately a love rectangle) at the heart of the film, a peculiar sci-fi adventure about an alien invasion that’s light on mindless violence, explosions and spaceships and heavy on character development and sentiment.

The object of the men’s affection is a spirited, willful young woman in her early 20s played by the remarkable 18-year-old Irish actor Saoirse Ronan (“Hannah,” “Atonement”). But she’s not actually an object of desire. She’s two people inhabiting the same body.

Born Melanie Stryder, Ronan’s character was a child when a race of tiny aliens named Souls descended on the Earth and used human bodies as their hosts, in the process killing the host’s persona.

An independent film coproduced by Meyer, “The Host” is directed with a sure hand by Andrew Niccol, whose edgy, thoughtful sci-fi films include “Gattaca” and “In Time.”

Meyer, 39, said she handpicked Niccol, who won an Oscar nomination for writing Peter Weir’s prophetic dystopian fantasy “The Truman Show.” “Andrew came up with the screenplay that was really lovely,” she said, “and it focused on character more than anything else.”

Meyer and Niccol enjoyed the best of both worlds: They made the film outside the studio system, but with a healthy $40 million budget.

“The Host” picks up and fleshes out some of the more interesting themes raised in the “Twilight” series. It poses some lofty questions about the nature of identity – are we our bodies or our minds? It inquires into the nature of love and our responsibility to our planet.

“The Host” “examines the idea of how we take for granted our bodies,” said Meyer. “It really makes you stop and appreciate having a functional body. I mean, when you think about all the things we can do, all the senses we have, it really makes you feel a lot of gratitude.”

Meyer’s film swings into action when Melanie, who has been on the run from the aliens with her lover Jared (Irons), is caught by Terra (Diane Kruger), a rather fanatical member of Seekers, the aliens’ version of the police force.

Melanie is forced to become a host for a very interesting Soul named Wanderer. Trouble is, Melanie’s inner self survives, and the two personas struggle for control.

One thing that deeply disturbs Melanie, Meyer said, is the aliens’ kind, peaceful demeanor.

“The aliens aren’t monsters who come in and kill everybody,” said Meyer. “What makes this book different, what is unusual, is that the bad guys don’t really seem bad.”

In fact, the Souls invaded Earth out of love – for the planet Earth, which they felt was being destroyed by humans.

“They judged us and condemned us and decided we didn’t deserve the Earth,” said Meyer. “And honestly, from a distance, you probably could make the same call.”

Ironically, it’s the humans who display the most violence in “The Host,” including a group of survivors led by Melanie’s uncle, Jeb Stryder (William Hurt), who live in an elaborate system of caves in New Mexico.

When a self-divided, confused, frightened Melanie shows up at the cave, she’s treated as a prisoner of war. Jared slaps her violently when she claims that she’s both Melanie and Wanderer and that she still loves him.

“I know a lot of people had said that (Jared) treats her badly,” said Irons, 27, whose father is Oscar-winning British actor Jeremy Irons.

“I think the kind of pain (he feels) is unimaginable. First, you lose all your family … then you find someone you can love, someone who personifies everything that you loved about the world. Then you lose her, too.”

A slap seems mild, said Irons, given the situation: “After all that loss, then having her come back — as an alien — to be there as a constant reminder of that pain.”

Yet Jared’s friend Ian (Abel) feels differently, and he does the unthinkable: He falls in love with the alien inside Melanie, squaring one of the most awkward, singular love triangles in recent movie history.

Abel, 25, best known for his role as Luke Castellan in the “Percy Jackson” film series, said he was stunned by Ronan’s ability to project two different personas on camera.

“For such a young person, she is insanely gifted and intuitive,” he said. “It just makes your job so much easier.”

If Meyer’s “Twilight” films are any indication, “The Host” may very well transform Ronan into an international megastar.

Meyer initially felt the actor was too young to carry the weight of the story.

“Then I saw ‘Hannah,’ and it completely changed my mind,” said Meyer. “She has an emotional maturity that really kills me.”

Meyer, who planned “The Host” as the first of a trilogy, said Abel, Ronan, and Irons all will be back for the sequel.