It's important to get the details of the three sons of the late Comte de Valmy straight in order to understand the plot:
Etienne - the oldest brother, now deceased, and father of Philippe
He inherited the Chateau Valmy and a Paris mansion.
He and his wife and son lived in Paris while his younger brother Leon managed his main property: the Chateau Valmy.
Etienne and his wife died a year ago, leaving Philippe an orphan. Linda is to be his new governess.
Leon - the middle son, and father of Raoul
He inhertied Bellevigne Manor, which is managed by his 30 year old son Raoul.
Leon managed Valmy for his brother, Etinne, who lived in Paris.
He has lived at Valmy his entire life.
A strong, enigmatic character, he has been confined to a wheelchair the last 12 years of his life.
Hippolyte - the youngest son with no children
Hippolyte inherited the Villa Mireille a few kilometers from the Chateau Valmy.
His job as an archeologist takes him from the Villa Mireille where he usually resides.
He is the co-guardian of Philippe who lives with him when he is there.
Notes on the map above
Paris
Linda came from London, England and traveled to Paris, London.
Paris was not only her prior home, it was also the location of one of the estates where Philippe grew up until his parents' death. Raoul also has an apartment there.
Soubirous
The main action is at the Chateau Valmy near the village of Soubirous in the Savoy province.
The village is apparently fictitious, or its name has changed, but it's approximately location is indicated by the gray dot.
Thonon is a real town near by.
Thonon
Thonon is on Lac Leman (also known as Lake Geneva.)
The Mireille Villa is lake-front property, only two kilometers from the Chateau Valmy. It is the home of Hippolyte.
Provence
Raoul's manor, Bellevigne, is in Provence. The location in Provence is not given.
Nine Coaches Waiting
Get the low-down, deep-dive, in-the-know analysis of Mary Stuart's Gothic novel.