Wisdom's Way / Coastal Murder

Four elderly ladies are found dead on the beach between Montgomery's Point and Howes End. None of them seem to be connected, just random killings. Could there be a serial killer on the loose, or is there another reason for their sudden demise? There is no CCTV evidence, and the forensic evidence is of little help at first, to help the team discover why the victims would leave their homes in the early hours of the morning, dressed only in their night attire, and seemingly just go for a walk? And where did the little silver dog come from?