PARK CITY, UTAH -- "Z for Zachariah" director Craig Zobel instructed one of his three actors Chris Pine to try multiple scene takes, to be "mean, meaner, creepier." Oscar nominee Chiwetel Ejiofor had to "delicately" expose his character's insecurities through a mention of race. And, believe it, "Wolf of Wall Street" actress Margot Robbie had to get awfully awkward for her role.

This is all to say: playing one of the last people on the planet to survive after an apocalyptic event is no walk in the park.

Robbie's Ann thinks she's Earth's sole survivor until a scientist Loomis (Ejiofor) stumbles into her scene. The two characters deal with "the delicateness of having to engage with people, knowing... that these are the only people you'll have to deal with forever" until Pine's younger, whiter, Christian-mischievous Caleb comes on the scene.

"I play the antagonist, [but] it was more interesting to play a character that was a bit more ambiguous," "Star Trek" lead Pine told HitFix during our interview at Sundance this week. "I had a great time noodling these people."

"It all felt very real, what we were going for in the dynamic of these relationships," Ejiofor said about the "bleakness" of the characters' reality.

Ann, as a character, found herself doing more than merely surviving, with Caleb and Loomis subtly vying for her affections. Robbie's character's journey turns into a coming-of-age tale, erupting out of a formerly religious and lonesome environment. 

"The [only] relationship she could mirror was her parents'," Robbie said on Ann's odyssey from  unfeminine head of her own household to a soft, dress-donning caretaker.

Watch our complete interview above on "Z for Zachariah," which plays all week during the 2015 Sundance Film Festival. Below is a continued chat on the film, with "Compliance" director Zobel on his actors for this film.

After five years as a columnist and editor at Billboard, Katie Hasty joined HitFix in 2009 for music and film reporting out of New York. The Midwest native has worked as a writer, music promoter and in A&R since 1999 and performs with her band Numbers And Letters.