A new documentary investigates a 250-year-old musical mystery. For the first 16 years of her life, Mozart's sister shared equal billing with her brother. Musical partners and collaborators, Wolfgang Mozart and Maria Anna Mozart played together before kings and queens, and were the talk of Europe. Forced to withdraw from public life because she was a woman, a stunning new investigation explores why she was retired and what happened to her music. Mozart's Sister is a 'musical-true crime' story that explores the lost talent of Maria Anna Mozart.