A bitter family feud over John Steinbeck’s estate escalated this week, when a Los Angeles jury awarded the novelist’s stepdaughter, Waverly Scott Kaffaga, $13.15 million in damages in an intellectual property dispute. The defendant plans to appeal.

Ms. Kaffaga filed the suit against the author’s son, Thomas Steinbeck, and his wife, Gail Knight Steinbeck, in 2014. She was seeking to recover what she claimed were lost profits from film adaptations of “The Grapes of Wrath” and “East of Eden,” as well as punitive damages. She argued that she had inherited rights to the author’s estate from her mother, and that the couple had interfered in studio plans to develop films and had hurt the estate financially. She sued the couple and their company, the Palladin Group.

The large sum awarded by the jury is the latest twist in a dispute that has dragged on since the author’s death in 1968, when he left most of his estate to his third wife, Elaine Steinbeck, directing that profits from his work go to her. He left his two sons, Thomas and John Steinbeck IV, from a previous marriage $50,000 each. (John IV died in 1991, and Thomas died in August 2016.)

In the years since, different family factions have taken their grievances to court, and hardly a decade has passed without a major legal scuffle. A 1983 settlement directed that royalties would be split among Elaine and Steinbeck’s sons, and Elaine would retain full control over the “exploitation” of his works, including any film and theater adaptations.