In 1977, Innes Haldane was one of seven extremely dysfunctional teenagers incarcerated in the Unit, an avant-garde psychiatric hospital on the outskirts of Edinburgh. There, she and her fellow inmates were forced into each other's lives, exposed to each other's pasts, and now share a collective memory.

Since then, they have spent their adult lives trying to forget the unspeakable acts that sent them there and the terrible secret that occurred behind its walls . . . until a message on Innes's answering machine with a voice from the past interrupts the quiet life she has tried so hard...