In the television adaptation of Cards on the Table, Mrs. Oliver and Poirot have a conversation about the mysterious Mr. Shaitana at an art exhibit.
Mrs. Oliver: “Oh look, it’s Mr. Shaitana. What is he? An Armenian? A Greek?”
Poirot: “No one knows. All that is known is that he is one of the richest men in London.”
After the murder is committed, Mrs. Oliver has plenty of theories about a motive for her (then-) favorite suspect, Dr. Roberts. “Ideas? Ideas? I’ve at least five. For example… say Shaitana was a moneylender, Roberts was in his clutches… or, Shaitana ruined his daughter. Or his sister, if he had a sister… or, or, Roberts is a bigamist and Shaitana knew it… or, how about this: Roberts secretly married Shaitana’s long-forgotten second cousin and stands to inherit a fortune in Syrian gold…”
The background of Shaitana is supposed to be a mystery unknown to the general public. But Superintendent Wheeler will later reveal the fact that he knows this detail, which causes Poirot to suspect that Wheeler may have been on closer terms with Shaitana than he had previously let on.
Constable: “Perhaps he was Egyptian?”
Wheeler: “No, he was Syrian.”
Poirot: “How do you know this?”
Wheeler: “It’s in the files.”
So Shaitana is Syrian… and Mrs. Oliver’s reference to “Syrian gold” in her brainstorming cannot possibly have been mere coincidence. How on earth did she know this detail about Shaitana and when did she find out?