After the sudden death of his father and a move to Italy, 14-year-old Joe loses his way and gets addicted to heroin.
"La Luna" tells the story of the recently widowed American opera diva Caterina Silveri. She takes her teenage son Joe, who believes that it was his father who died, while in reality it was his stepfather, with her on a long singing tour to Italy. But she is so absorbed by her hectic work schedule that she doesn't pay much attention to him. Soon she discovers that her troubled and lonely son has become a heroin addict and in her attempts to get him of the drugs, they start an incestuous relationship. Still, these problems may also result in a meeting between Joe and his real father, whose existence she has always kept a secret, but now reveals in a desperate attempt to make her son act normal again.