Charlotte was supposed to be looking after the children, and she swears she was. But while her three kids are all safe and sound at the school fair, Alice, her best friend Harriet's daughter, is nowhere to be found. Frantically searching everywhere, Charlotte knows she must find the courage to tell Harriet that her beloved only child is missing--and admit that she's solely to blame.

Harriet, devastated by this unbearable loss, can no longer bring herself to speak to Charlotte again, much less trust her. Struggling to keep her marriage afloat, Harriet is more isolated than ever. But as the police bear down on both women, trying to piece together the puzzle of what happened to this little girl, dark secrets begin to surface--and Harriet discovers that trusting Charlotte again may be the only thing that will reunite her with her daughter...

"A chilling, captivating story of friendship, motherhood, and deceit" (Megan Miranda, New York Times bestselling author), Her One Mistake will keep you guessing until the very last page.