Grey Stones (A Jess Bridges Mystery, Book 4) by Joss Stirling
DI Leo George has been invited to a friends' reunion weekend at a lodge in the grounds of the exclusive Piccadilly Club in the affluent Cotswolds village of Chipping Norton. He's bringing his new girlfriend, Jess Bridges, an edgy private detective who's wondering if she'll fit in with Leo's old university set.
As the only outsider, it's clear to Jess that there is more than just friendship at the heart of the group, and they seem to have made a habit of pushing the boundaries of their relationships to their limits. The weekend proves to be a catalyst that opens a Pandora's box of ugly secrets - Jess can see that when some friendships are this toxic, there can only be one deadly outcome ...