A screen adaptation of Ruth Rendell's Tree of Hounds, Betty Fisher tells the story of three mothers, all of whom are very different from one another but bonded inextricably by a shared drama. The first mother is Betty, a promising young writer who has a four-year-old son, Joseph. The second is Carole, a bar waitress whose difficult life leads her to mistreat her son, José. The third mother is Margot, Betty's mother, who re-enters her daughter's life after an extended absence. When Joseph is killed in an accident, Margot schemes to prove her love to her grieving daughter. Fate subsequently intervenes, and the three mothers find their lives woven together in a web of suspense and intrigue.