Zadie and Emma have been best friends since their early twenties in medical school. Now they're happily married wives and mothers with successful careers - Zadie as a paediatric cardiologist and Emma as a trauma surgeon. Their lives are chaotic but fulfilling, until the return of a former colleague unearths a secret one of them has been harbouring for years. It becomes evident that Emma must have known more than she revealed about circumstances that nearly derailed both their lives during medical school, and Zadie starts to question everything she thought she knew about her closest friend.