The discovery of a blood-soaked four-year-old girl walking alone on the roadside leads detectives Hill and Walker to the scene of a bloody massacre that has left an entire family dead, save the young girl and her injured father. The investigation is particularly hard on Harriet as it takes her back to the recent murder of her husband Matt. To make matters worse, she has learned, second hand, that the DPP has consented to drop the murder charge against the woman accused of the crime in exchange for a guilty plead to the lesser charge of manslaughter. On the verge of a breakdown, Harriet must stay focused as she and her colleagues work to locate a killer.