Documentaries often focus on social issues in dire need of change or stunning depictions of nature, but it takes true fortitude for a filmmaker to make a documentary about themself. Sarah Polley's “Stories We Tell” does just that, exploring the unusual circumstances of Polley's parentage in an unflinchingly honest and fascinating fashion.

Polley breathlessly plunges into her story, asking members of her family and other relevant parties to tell the story of her parents' marriage and the time her thespian mother spent in another city for a role. When she returned, pregnant with Sarah, it was assumed that the conception occurred during a visit with her husband, although the possibility of Polley being fathered by one of her mother's co-stars becomes a running joke in the family. Eventually, Polley decides to investigate for herself.

The film is more mystery than memoir, and despite its intensely personal nature, Polley lets her story unfold with dramatic reveals aplenty. Supplementing interview footage with recreations of her family's past and voiceover from the man who raised her, Polley stages her story with thoughtful evocations of nostalgia and memory, touching on fascinating thematic territory through a deeply subjective lens. The documentary's first half is something of a shell game, shuffling various players and potential parents around before blindsiding the audience with a masterfully deployed twist.

From there, “Stories We Tell” gets increasingly self-reflexive, and Polley finds fascinating, candid truths in the way her family reacts to her big news and her choice to broadcast her findings to a widespread audience. As Polley examines the human, relatable ways the people around her absorb her findings and interpret the memories they all share, she also explores and excavates some of the underlying tensions and themes of her own work.

“Stories We Tell” is the rare documentary that indulges the director's personal life in painstaking detail without ever becoming overwrought or self-impressed. A lot of that has to do with the effortless wisdom and nuance that has graced all of Polley's work, not to mention her gorgeous, wryly composed narration and her insightful, precise direction and editing. But mostly, it's because “Stories We Tell” is a wholly compelling work of stunning courage and grace, and one of the best films of the year.