Schoolteacher Ellie Manning hears the devastating news that her husband Greg has been killed in a car accident, and her grief is compounded when police tell her that Greg did not die alone – another woman, Milena Livingstone, was in the car with him. Faced with the shattering knowledge that Greg was having an affair, Ellie is determined to discover everything she can about Milena. Ellie's best friends Gwen, Fergus and Joe rally to help, but are unable to stop her obsession with the woman who died with Greg.