The conclusion of a two-part special taking viewers behind the scenes of a police investigation into the death of an 11-week-old baby. Both the mother and her partner are under suspicion of inflicting injuries on the child on a similar scale to those suffered in the notorious case of Baby P, but neither is yet in custody. DI Lucy Thomson of Cambridgeshire's Major Crime Unit, who leads the investigation, has decided she isn't ready to show her hand. However, when police receive a 999 call reporting a disturbance at the couple's flat they rush to the scene and the investigation takes a dramatic turn.