I read about this in the Agatha Christie newsletter and at first I thought it was a typo. I thought they meant the Miss Marple story, "Greenshaw's Folly." Further investigation in the newsletter revealed the exciting details:
https://www.agathachristie.com/stories/hercule-poirot-and-the-greenshore-folly"Written by Agatha Christie in 1954 to help raise money for her local church at Churston Ferrers, The Greenshore Folly novella was ultimately never published in its original form. Instead, it became the basis for one of her favourite novels, Dead Man's Folly, and a Miss Marple story was written for the church.
Marking 60 years since it was written, this previously unpublished version of the story is introduced by Tom Adams, whose intricate paintings graced Agatha Christie's paperback covers throughout the 1960s and 1970s, and who has painted the remarkable new jacket for the book. It also includes a preface by Agatha Christie's grandson, Mathew Prichard, and an insightful afterword about the writing of the story by the renowned Christie expert, Dr John Curran."
My copy arrived today and it's next up on my reading list:
"Hercule Poirot And The Greenshore Folly
An urgent telephone call summons Poirot to Devonshire on what Miss Lemon declares is a "wild goose chase". The caller is the eccentric detective novelist, Mrs Ariadne Oliver, and the reason for her alarm seems based solely on woman's intuition. Is the fictional murder scenario she has been asked to devise a cover-up for something more sinister? And what is the significance of the Greenshore Folly, an architectural embarrassment in the sweeping grounds of the otherwise impressive Greenshore House?"
