On a beautiful summer’s night 20 years ago, troubled 17-year-old Tamara Drayton was found floating face down in the pool of her family’s idyllic mansion in the south of France, leaving her twin brother, golden-boy Blake, to pick up the pieces of their shattered family. Also left behind was their sister, Nina; at six years old, she became the youngest person ever to testify in a French murder trial. She’s the only one who saw what happened --- who watched as her babysitter, Josie Jackson, pushed Tamara under the water and held her there until she stopped breathing. Didn’t she? Twenty years later, Nina's memories have faded, leaving her with no idea of what really transpired that night. When a new true crime documentary about her sister’s murder is announced, Nina thinks this might be her chance to finally find out.

Rachel has been in love with Alistair for 15 years. Even though she’s now married to someone else. Even though she was a teenager when they met. Even though he is 20 years older than her. Rachel and Alistair’s summer love affair on a remote, sun-trapped Greek island has consumed her since she was 17, obliterating everything in its wake. But as Rachel becomes increasingly obsessed with reliving the events of so long ago, she reconnects with the other girls who were similarly drawn to life on the island, where everyone acted in ways they never would at home. And as she does so, dark and deeply suppressed secrets about her first love affair begin to rise to the surface, as well as the truth about her time working for an enigmatic and wealthy man who controlled so much more than she ever could have realized.