SOLVED. Fiction. A group of people form unlikely friendships at a week-long creative writing retreat [s]

[Madeleine]

I started reading this in 2010-2012 (it may be slightly older). I was in the middle of moving house, and it got lost along the way, and I was halfway through, and it's driving me crazy! The edition's front cover is a rendered house with a window and a purple-flowered climbing plant.
One of the main characters is the niece of the owners of the retreat (whose name I can't remember). I do, however, remember one character called Marnie (who comes from a wealthy family from the US, and another called Christopher ( who is haunted by an accident where he hit someone with his car while drunk). The book starts with a flashback of a young child around 4-5 years old talking with an eccentric lady in the Caribbean. The rest of the story is set in England (I think)

[Tab]

Secrets and Shadows

[Madeleine]

That's the book!! Thank you so much!