The book "Ordeal by Innocence" was dedicated "To Billy Collins with affection and gratitude." It was Billy who had convinced Christie to leave her one-sided deal with the Bodley Head, the publishers of her first six books, and to switch to William Collins Sons & Co in 1926. Now known as HarperCollins, they remain Agatha Christie's UK and US publishers.
When Anna Chancellor was young, she attended a convent, where she was not allowed to watch TV except on Feast days. She said "More or less, they were always Agatha Christies. And I loved them."
Ella Purnell used to play piano when she was a kid, but it took her three months to learn the five bars of Chopin's Nocturnes that she plays in the show.
Anna Chancellor didn't want to wear florals as her character, Rachel. She said "it made her feel fulsome and a bit sexy, and I felt she should be much more military [and wear more] tailored, controlled suits."
Many of the costumes were originals that were sourced from around the world, including Italy, France, London and Glasgow. Some of the costumes were created for the show or modified to make them more 1950s.