The creepiest line in Netflix’s ‘The Whisper Man’ came from writer Alex North’s own living room.

He was in the kitchen when he heard his young son playing alone, poked his head in to ask what he was up to, and got the answer that changed his book: “I’m just playing with the boy in the floor.”

North had set out to write about fathers and sons but couldn’t find the way into a crime thriller. That moment gave it to him. “I knew then that the boy in my story would have imaginary friends like that, and that a few of them might turn out to be more than they seemed,” he told Australia’s Better Reading blog.

He built the rest from online parenting forums where people trade the unsettling things their kids say. A child pointing at a graveyard and saying “that’s where I used to live.” A child describing the man with the long neck in the closet, before the parents learn someone hurt themselves in the house years earlier.

The novel became an international bestseller. Netflix’s adaptation stars Robert De Niro as a retired detective pulled back in when his 8-year-old grandson is abducted, with Adam Scott as the boy’s father and De Niro’s estranged son. The trail leads back to a child predator De Niro’s character put away 30 years ago, who now seems to be active again.

