Thursday's Children by Nicci French

Frieda Klein is uninterested in catching up on old times when her former classmate, Maddie Capel, shows up at her door—until she hears about Maddie’s troubled daughter, Becky. The teenager claims she was raped in her own bed one night while her mother was downstairs. Her assailant left her with a warning: “Don’t think of telling anyone, sweetheart. Nobody will believe you.” And no one does—except Frieda.
 
Becky’s story awakens dark memories of an eerily similar incident in Frieda’s own past that she’s been avoiding for decades. When Becky is found hanging from a beam in her bedroom, Frieda returns home, seeking out her old high school friends to ask what they remember about the night that prompted Frieda to leave town for good. But confronting the ghosts of the past turns out to be more dangerous than she ever expected.