This is a disquieting and ambiguous movie in a classic US indie style. It may not be entirely perfect – I sat down to it twice before fully hearing its insistent, sinister whisper – but there's an unsettling darkness in the deep green, sun-dappled shade of its woodland locations. Sarah Paulson plays Lucy, married to a wealthy, priggish Brit called Ted (Hugh Dancy), and currently on vacation in their huge, lakeside home. Out of the blue, she receives a payphone call from her troubled younger sister Martha (Elizabeth Olsen), from whom she hasn't heard in years, demanding to be picked up from somewhere in upstate New York. Martha comes to stay, and it becomes clear she has escaped from a cult run by a deeply scary Mansonesque guy called Patrick – a chilling performance from John Hawkes – who had the creepy mannerism of renaming all his devotees as a way of establishing psychological ownership: Martha's new name was "Marcy May". Flashbacks cleverly and indirectly disclose the repeat patterns of abuse and dysfunction that have damaged Martha's mind. She is terrified and paranoid about being tracked down, perhaps with reason. Having tried one night to call one of her friends at the cult's remote farmhouse HQ from Lucy's house phone, she realises too late that this has enabled the "callback" option, and perhaps allowed the cult to find her. The question of why she was able to escape so easily in the first place leaves a queasy slither of fear: have they, in fact, allowed her to escape? It's acted and directed like a sensitive drama, rather than a scary movie, and is all the scarier for it.