Chloe stars as Annika, a teenager who befriends Keira's 28-year-old Megan, a young woman who recently broke up with her long term partner and has floundered in her career.
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Seeking somewhere to temporarily escape to, Megan moves in with Annika and her single father (Sam Rockwell).
Speaking about working with Keira at Sundance Film Festival in 2014, Chloe revealed: "I have been a big fan of Keira since I was a kid, I watched Pride and Prejudice every day.
"So when I had the pleasure to work with her, I was really excited."
Keira added of the film: "I loved the simplicity of the story and through it the complexity, it's very true to human nature... It's the stuff that life is made of."
Chloe has recently been rumoured to be dating Victoria and David Beckham's son Brooklyn, and in a recent interview finally addressed the rumours during an on Watch What Happens Live this week.
While taking call-in questions, Chloe was asked by a viewer if she and 15-year-old Brooklyn are more than just friends.
Chloe Moretz and Brooklyn Beckham step out together at a Jay-Z concert
"I don't know. He's a very good guy and he's a good person. I enjoy with him." Her host Andy Cohen then asked if she simply didn't want to "put a label on it". "Maybe," she replied.
Chloë and Brooklyn have been spotted together a number of times over the summer – in August alone, they attended the Teen Choice Awards together, were seen at an Ed Sheeran concert in LA, and Brooklyn supported Chloë at the premiere of her new film, If I Stay.
Say When, which has been titled Laggies in the United States will be released in the UK on November 7th.