For most of Sylvie Bianchi’s life, the records of her grandmother’s time as a prisoner in the Ravensbrück concentration camp seemed too painful to examine. Sylvie kept her grandmother’s letters, diaries, photographs and home movies in the attic of her family’s French farmhouse for decades. The documentary “Nelly & Nadine” captures the story as Sylvie finally opens dusty boxes, unearthing a surprising tale of love and resilience. Sylvie learns that her grandmother, Nelly Mousset-Vos, was an opera singer turned spy with the French Resistance. She was imprisoned at Ravensbrück in 1944, and there, Nelly met Nadine Hwang, who had worked in literary circles in Paris and likely participated in resistance efforts. The pair fell in love. They were separated, but after the war, Nelly and Nadine moved together to Venezuela. They lived as a couple until Nadine’s death in 1972, and Nadine documented their lives together in home movies that are shown in the film. In informal, pensive interviews with the director Magnus Gertten, Sylvie reflects that she remembers Nadine, but Nadine was only ever referred to as her grandmother’s friend and housemate. It’s an astonishing love story, all the more notable for the sheer amount of documentation that is shown onscreen. Gertten first identifies Nadine in newsreel footage of refugees arriving in Sweden after the liberation of the camps. This footage alone, which captures hundreds of joyful faces – and Nadine as a solitary somber figure in the crowd – would be noteworthy. But it’s equally miraculous that Nelly and Nadine’s records were preserved by Nelly’s family – an archival kindness that is, historically-speaking, not frequently afforded to women who love other women. The film is moving for the intimacy it depicts, an archive as unlikely as the love story itself.