On Christmas Eve, 1944, in the Ravensbrück concentration camp, the renowned Belgian opera singer Nelly Mousset-Vos was ordered to sing Christmas Carols. Partway through her performance, fellow inmate Nadine Hwang shouts out a request from “Madame Butterfly.” After singing the aria, Nadine emerged from the darkness and kissed her. From that moment on, the two were as one. Despite being separated during the final months of the war, Nelly and Nadine managed to reunite and would go on to spend the rest of their lives together. For many years their love story was kept a secret. Now, Nelly’s granddaughter, Sylvie, has decided to open Nelly and Nadine’s unseen personal archives to share their story. Through incredible home movies, letters, rare photos, and other personal memorabilia, director Magnus Gertten reveals an epic tale that spanned decades.