The chateau : a novel / Jaclyn Goldis.

Enhanced descriptions from Syndetics:

A dream girls trip to a luxurious French chateau devolves into a deadly nightmare of secrets and lies in this "twisty, well-paced murder mystery that never fully lets go" (Sarah Penner, New York Times bestselling author).

Welcome to picturesque Provence, where the Lady of the Chateau, Séraphine Demargelasse, has opened its elegant doors to her granddaughter Darcy and her three friends. Twenty years earlier, the four girlfriends studied abroad together in France and visited the old woman on the weekends, creating the group's deep bond. But why this sudden invitation?

Amid winery tours, market visits, and fancy dinners overlooking olive groves and lavender fields, it becomes clear that each woman has a hidden reason for returning to the estate after all these years. Then, following a wild evening's celebration, Séraphine is found brutally murdered.

In the midst of this shocking crime, a sinister Instagram account pops up, exposing snapshots from the friends' intimate moments at the chateau, while threatening to reveal more.

As they race to uncover who murdered Séraphine--and is now stalking them--the friends begin to suspect each other. Because the chateau houses many secrets...several worth killing for in this "mesmerizing story of betrayal and revenge" (Megan Collins, author of The Family Plot ).