Babygirl — the erotic thriller starring Nicole Kidman as a CEO who puts her career and family on the line for an affair with a young intern (played by Harris Dickinson) — features a surprising Christmas backdrop, which writer-director Halina Reijn reveals was a last-minute, thematic pivot.

“I wrote it as a summer movie, it was all going to take place in the Hamptons and it was going to be on the beach,” she told The Hollywood Reporter at the film’s Los Angeles premiere on Wednesday. “Then the strike happened, of course it was pencils down and we had to wait, and then the schedule became Christmas. And I was like, ‘We should definitely make this into a Christmas movie,’ and after the strike, I just rewrote the whole thing to Christmas.”

Many of the scenes feature elaborate Christmas trees and holiday music, as Reijn added that the change “had such...