I'm not sure this book should be categorized as a mystery, but there is a death to be solved - so it more or less fits into the genre.
The story: Ruth and Mark Ardingly are looking to get out of London for two major reasons. Mark, a lawyer, has a damaged reputation because he was accused - though exonerated - of looking at child pornography; and Mark always dreamed of farming. So the Ardinglys purchase a property called The Well on a hilltop in the English countryside.
Oddly (to say the least) The Well has plenty of water and rain when the rest of England is suffering from a ruinous drought. The drought has made food scarce and put people out of work. Thus, desperate people resent the Ardinglys' green oasis and accuse the couple of all manner of nefarious deeds, including stealing water and using witchcraft.
To stop a mass invasion of their property, the Ardinglys close it off with fences and gates and get police protection. The couple do, however, let their semi-estranged daughter Angie camp on the land with her five-year-old son Lucien and a group of 'travelers' (hippies). Before long the nuns of a religious cult called 'The Sisters of the Rose' also insinuate themselves onto The Well property. The group's leader, Sister Amelia, convinces Ruth she's the 'chosen one' who's responsible for The Well's water.
The presence of the nuns causes big problems. Ruth starts spending a lot of time with them, praying and spreading their gospel. Moreover, Sister Amelia wants The Well to be inhabited solely by women. She has no use for men and influences Ruth to become estranged from Mark. Sister Amelia even resents Ruth's grandson Lucien - whom Ruth adores - because he'll eventually inherit The Well.
Living conditions at The Well becomes fraught: the government takes an interest in the property; the Ardinglys become isolated because the townsfolk hate them; Mark and Ruth fight with each other and with their daughter Angie; Ruth becomes overly enamored with the The Sisters of the Rose; and so on. And then one day Lucien is found dead and Ruth is accused of killing him - perhaps while sleepwalking.
The story is told from the point of view of Ruth who's now under house imprisonment at The Well. In the present, Ruth - besides being devastated by Lucien's death - is alone and lonely. She has no communication with her family and the nuns are long gone. The only people Ruth speaks to are her guards and occasionally a priest. Ruth spends most of her time either sleeping or thinking about the events that led to her current dire situation - attempting to figure out what really happened to little Lucien.
The author writes beautifully, with lush descriptions of the landscape and engaging characterizations of Ruth, Mark, Angie, Sister Amelia, the other nuns, the priest, the guards, etc. That said, I didn't enjoy the book. it was too long and there was too much praying and proselytising by The Sisters of the Rose - which became tedious. I also thought the solution of 'the mystery' of Lucien's death was predictable. A proper police investigation would have exposed the culprit in a jiffy.
What I really hoped was that the author would address the mystery associated with The Well's abundant water supply but she didn't. Just not the book for me.