Throughout the 'Doctor Who' episode "The Unicorn And The Wasp", actual titles of future Agatha Christie mysteries were incorporated into the dialogue of various characters; the inference being that even though most of her memory of that weekend was lost to amnesia, still Mrs. Christie remembered fragments that would find their way into her later work. (Of course, how she could have known about phrases like "dead man's folly", which were spoken in "downstairs" conversations, is a detail that was glossed over - much like how Lady Eddison planned on explaining three deaths at her estate, including her own son.)
In some cases, it was the situation which later turned up in one of her plots, like the use of a wasp's sting as a possible murder weapon.
And then there was Donna's mention of Miss Jane Marple, who had not yet appeared in a Christie mystery, and Donna's mention of "Murder On The Orient Express". Mrs. Christie was intrigued by both ideas, so that it could be said Donna Noble was her muse for both.
I'll be dealing with Agatha Christie sharing the TV Universe with her creations in a later post. But as for "Murder On The Orient Express", it has not been adapted for Earth Prime-Time yet, and may never be.* So it could be said that - for now - "Murder On The Orient Express" is a fictional story Christie wrote about a "real" detective.
So these are the titles that were referenced in "The Unicorn And The Wasp":
"Cards On The Table"
"Appointment With Death"
"They Do It With Mirrors"
"Cat Among The Pigeons"
"Dead Man's Folly"
"Taken At The Flood"
"The Murder At The Vicarage"
"Death Comes As The End"
The following titles were actually named as being her stories:
"Murder On The Orient Express"
"Death In The Clouds"
"The Murder Of Roger Ackroyd"
These titles served as plot points:
"The Body In The Library"
"The Secret Adversary"
"The Man In The Brown Suit"
Wikipedia lists this last batch of titles as being cited for this episode, but I don't know where, how, or why:
"Why Didn't They Ask Evans"
"N Or M?"
"The Moving Finger"
"And Then There Were None"
*The modernized 2001 version of "Murder On The Orient Express" with Alfred Molina as the Belgian detective must be situated in an alternate TV dimension. Surely it must be accepted that as far as the main Toobworld is concerned, David Suchet IS Hercule Poirot.