Margot Robbie's character thinks she's the only survivor until she meets Chiwetel Ejiofor's scientist. She says she was continually put into awkward positions during filming. "Just delving into it deeper," she says. "And I guess, for this role specifically, I tried to remember how I behaved when I was a younger teenager. I didn't know how to act cool around guys or how to regain some sort of power if somebody told me off. Those were the things I was trying to focus on this character."

Chiwetel Ejiofor, Chris Pine & Morgot Robbie lead the cast in Z For ZachariahChiwetel Ejiofor, Chris Pine & Morgot Robbie lead the cast in Z For Zachariah

For his part, Ejiofor had to react "delicately" to reveal his character's insecurity. "It all felt very real," he says of the relationship dynamic. "Craig can breathe life into the relationships of a very small number of people kind of effortlessly!"

Ejiofor relished the challenge. "This is an acting exercise," he says, "ratcheting up the tension and the drama of it, just in the force of these people. They're not particularly archetypal; there's a regularness to them that becomes an unbearably tense dynamic. And I loved that."

He particularly enjoyed his and Robbie's "complicated dance of friendship and perhaps romance, and then it turns into something slightly darker once the arrival of another person alights insecurities and fears and worries and tension." This third person is Pine's younger and more mischievous character. Zobel urged Pine to improvise a variety of tones in each take, getting "mean, meaner, creepier". "I play the antagonist," Pine says. "It was more interesting to play a character that was a bit more ambiguous. I had a great time noodling these people."

Pine especially liked working with such a small cast and crew. "I really enjoyed the intimacy," he says. "That size of a film lends itself to getting more interesting things oftentimes. You're just more comfortable. I also liked that Craig is not trying to please anyone. This is his film from A to Z."

Watch a clip from Z for Zachariah here: