I read Green Darkness as a teenager and never thought of it as anything other than fiction until I was planning a trip to England in 1993 and learned that many of the places in the book exist and can still be visited.
The story begins with Celia -- a young American woman, recently married to an English baronet who has feelings of deja vu when she visits certain places. After a disturbing incident with her new husband, she is cast into a physical state in which she relives a previous existence in 16th Century England.
There is danger for Celia in both her current physical state as well as the unresolved difficulties of her previous life, and in both lives, there is a somewhat knowledgeable and sympathetic character who tries to help her.
The Spread Eagle
Cowdray House is now in ruins, but there is enough left to imagine the place as it must have been when it was owned by Sir Anthony Browne, the first Viscount Montague -- another character in Green Darkness.
The ruins are haunting and evocative and it's easy to see how they may have inspired Anya Seton when she wrote Green Darkness -- especially the legend of Viscount Montague's curse.
Ightham Mote does indeed have a ghost story -- the body of a woman discovered in a walled up room--just as the story is presented in Green Darkness. The woman is thought to have been Dame Dorothy Selby whose misdirected warning letter alerted Parliament to the Gunpowder Plot.