Schoolteacher Ellie Manning (Anna Friel), happily married to accountant Greg, with whom she is eager to start a new family. However, Ellie's plans for a romantic dinner at home with her husband one evening are shattered when the police arrive to inform her Greg has been killed in a horrific car accident, along with an unknown female passenger. Was Greg having an affair? Who was the unknown woman? As Ellie digs deeper, she becomes convinced the crash was no accident but her obsession with discovering the truth leads those around her to question her emotional state. Meanwhile, Ellie, now unable to trust even her closest friends, is becoming suspicious of everyone, including herself.