Jason Reitman is never as good as when he’s collaborating with screenwriter Diablo Cody; bonus points if the film in question stars Charlize Theron, as Tully does. This unexpectedly searing film alternates between tender drama and psychological terror, plumbing the depths of an exhausted woman’s (Theron) psyche to explore exactly what it means to be a mother and all the sacrifices and trade-offs that entails. Theron is exceptional opposite a magnetic Mackenzie Davis, who plays the eponymous nanny, hired to help ease the stress of Theron’s life. Ron Livingston delivers an underrated performance as Theron’s absent-minded but good-natured husband, who – like so many men – is unaware of the extent of his wife’s emotional struggles. Not to sound reductive, but Cody has written what could be described as a psychological horror remake of Mary Poppins: an astonishingly poignant exploration of motherhood and the covenants one makes with herself to stay afloat. Tully isn’t as flashy as this season’s clear Oscar contenders, but that’s sort of what makes it special. It’s bracingly honest and refreshingly simple in its ambitions.