Sarah Polley’s two earlier features, Away From Her and Take This Waltz, were about what women are – or aren’t – prepared to settle for in marriage. This open-hearted, dramatic and extraordinary documentary is about her mother, Diane, who died when Polley was only 11. Using grainy Super 8 home-movie footage to illustrate filmed interviews with her family and with a gaggle of people who knew Diane, we learn early on that Diane had become the first woman in Canadian legal history to lose custody of her children when she left her husband for Sarah’s English dad, Michael Polley.

What stands out is not the everyday frustration that followed, at domestic confinement after having more children, and with her undemonstrative husband. What’s striking is their understanding, and the understanding of their friends, of how she handled it, and of a major revelation after her death. Sarah Polley, herself an actor from the age of four (you’ll probably recognize her face, if not her name), gives us, not a self-absorbed portrait of a luvvy family, but a wider, essentially human, insight. Into how people and circumstances make us what we are. Into how love and loyalty adapt and change, but persist.