Mainstream understanding of wayward nuns is often drawn from The Sound of Music (1965). Maria von Trapp’s inability to stick to the script while keeping her wimple on opens the time-old dilemma between selfhood and sanctity in the life of a bride of Christ. Pedro Kos’s Rebel Hearts (2021), which premiered at this year’s Sundance Festival, takes up the same theme, although the Sisters of the Immaculate Heart of Mary go much further in their transgressions than singing on hillsides and falling in love with handsome widowers. Threading the story of the Los Angeles sisterhood against the backdrop of the social and political upheaval of the 1960s and ’70s, the documentary attempts to locate the roaring advances of feminism, post-conciliar renewal, pacifism and pop-art, all within the cloistered world of the Hollywood faithful. Given the hydra-headed nature of its subject, the result is only partially successful.