The screenplay is an adaptation of Stefan Zweig’s novella Burning Secret, which Vulture describes as a reverse Lolita (plot summary for those who forgot high school English class: a man enters a relationship with a woman because of his obsession with her 12-year-old daughter). In Burning Secret, a man befriends an adolescent boy in order to seduce his mother. Zweig’s other works have inspired films like Wes Anderson's The Grand Budapest Hotel (which the director claims he "stole" from Zweig's novels Beware of Pity and The Post-Office Girl).
Kubrick’s screenplay adaptation is co-written by novelist Calder Willingham and dated October 24, 1956. Although the screenplay bears a stamp from MGM’s screenwriting department, Nathan Abrams—the Bangor University professor who discovered the script—thinks it’s likely the studio found it too risqué for mass audiences.
“The child acts as an unwitting go-between for his mother and her would-be lover, making for a disturbing story with sexuality and child abuse churning beneath its surface,” Abrams told The Guardian. It's worth noting, however, that Kubrick directed an adaptation of Vladimir Nabokov's Lolita in 1962, which MGM distributed, and it was also met with a fair share of controversy.
Abrams said the screenplay for Burning Secret is complete enough that it could be created by filmmakers today. He noted that the discovery is particularly exciting because it confirms speculations Kubrick scholars have had for decades.
“Kubrick aficionados knew he wanted to do it, [but] no one ever thought it was completed,” Abrams told The Guardian.
The Guardian reports that Abrams found the screenplay while researching his book Eyes Wide Shut: Stanley Kubrick and the Making of His Final Film. The screenplay is owned by the family of one of Kubrick’s colleagues.