Bitter Orange by Claire Fuller
From the attic of Lyntons, a dilapidated English country mansion, Frances Jellico sees them—Cara first: dark and beautiful, then Peter: striking and serious. The couple is spending the summer of 1969 in the rooms below hers while Frances is researching the architecture in the surrounding gardens. But she's distracted. Beneath a floorboard in her bathroom, she finds a peephole that gives her access to her neighbors’ private lives.
To Frances' surprise, Cara and Peter are keen to get to know her. It is the first occasion she has had anybody to call a friend, and before long they are spending every day together: eating lavish dinners, drinking bottle after bottle of wine, and smoking cigarettes until the ash piles up on the crumbling furniture. Frances is dazzled.
But as the hot summer rolls lazily on, it becomes clear that not everything is right between Cara and Peter. The stories that Cara tells don’t quite add up, and as Frances becomes increasingly entangled in the lives of the glamorous, hedonistic couple, the boundaries between truth and lies, right and wrong, begin to blur. Amid the decadence, a small crime brings on a bigger one: a crime so terrible that it will brand their lives forever.