January 1992. A baby girl is left alone for a moment. Long enough for a mother to dash into a shop. Long enough for a child to be taken.

Thirteen years later, solicitor Robert Knight's stepdaughter wins a place at a prestigious London school for the gifted. The only puzzle is his wife Erin's reaction. Why is she so reluctant to let Ruby go? Doesn't she want what's best for her? As Erin grows more evasive, Robert can't help but feel she has something to hide, and when he stumbles on mysterious letters, he discovers she has been lying to him. Somewhere in his wife's past lies a secret; a shocking secret that threatens to destroy everything...