In the first “Transformers” movie, it all seemed so simple: Boy meets impossibly hot girl, witty banter is exchanged, boy gets girl and giant robots attack. In “Transformers: Revenge Of The Fallen,” however, a bizarre love triangle disrupts the lives of Sam (Shia LaBeouf) and Mikaela (Megan Fox) — with some help from a mysterious new woman.

“She is playing more of the seductress,” explained Isabel Lucas, the sexy young Australian actress who plays Alice in “Fallen,” the blockbuster film currently breaking box-office records worldwide. “She’s got mysterious intentions that we don’t really know about towards him. He is obviously in a relationship and still with Mikaela at this stage — so he is resisting it quite strongly.”

Although millions of fans are pouring into theaters to see the massive robots of “Transformers,” this Mikaela/ Sam/ Alice conflict serves as a major component of the film’s human element.

“It’s not that Sam is turning his back on Mikaela,” explained LaBeouf, whose character meets Alice while at college. “It’s just that a priority for Sam at this point is not only a relationship, but trying to juggle him liking himself.”

“They’re trying to maintain a long-distance relationship, because Sam goes away to college and Mikaela can’t afford to go to college,” Fox explained of the duo’s relationship struggles. “She has to stay behind, and she’s working the grind at a chop-shop with her dad who is released from prison.

“He gets into some trouble at college — which is really innocent — but to [Mikaela] being so far away, being on the outside, it doesn’t seem as though it’s innocent,” she continued. “I go there to figure out what’s happening, and he’s in a sticky situation with a Decepticon. Then we get sucked up into this ongoing battle between the Autobots and Deceptions.”

But the entryway to all that action is Alice — a character who may similarly be more than meets the eye. “She’s a character that certainly causes some conflict,” said Lucas, flashing a sly grin. “She’s quite a layered character — you’re not quite sure of her intentions when she’s introduced.

“Shia is incredible to work with,” said the actress, best known Down Under as the star of the soap “Home and Away.” “He is so innovative in that he is always coming up with new ways to play the scene — he’s a real risk-taker and will throw himself off the cliff. He is very brave in that sense. … He’s carrying the entire film, he is very talented.”

Those who’ve already seen “Revenge of the Fallen” know the answer to Alice’s secret — but may still have one question left: How could a guy even think about cheating on a woman who looks like Megan Fox?

“Right … well … ” Shia struggled. “That’s totally understandable.”

Watch a video interview at MTV.com (not available outside the US, though)