Ich weiß, was du letzten Sommer getan hast
Influenced by her own interest in the supernatural and speculative fiction, Duncan wrote various suspense and horror novels aimed for teenagers. Some of her works have been adapted for the screen, the most infamous example being the 1997 film "I Know What You Did Last Summer", adapted from her 1973 novel of the same title. After the publication of "I Know What You Did Last Summer", Duncan wrote "Down a Dark Hall" (1974), a Gothic novel following four students at an isolated and mysterious boarding school. In 1976, she published the supernatural horror novel "Summer of Fear", which was also adapted into a 1978 film by director Wes Craven.