Luna (1979) on Netflix

While touring in Italy, a recently-widowed American opera singer has an incestuous relationship with her 15-year-old son to help him overcome his heroin addiction.

Recently widowed American opera diva Caterina takes her teenage son Joe with her on a long concert tour in Italy. Absorbed in her hectic work in various Verdi operas around Rome, Caterina is shocked to discover that her troubled, lonely son has become a heroin addict. Her desperate attempts to wean the youth off the drug result in an incestuous relationship, but also in a possibility to reunite Joe, and maybe herself, with his real father, whose existence she has kept secret from him.

—Markku Kuoppamäki