Based at police HQ in Dover, the small, under-resourced Missing Persons Unit is run by a charismatic woman detective: DS Mary Jane Croft, played by Pauline Quirke. Mary Jane and her story form the emotional heart of the series. MJ, as she likes to be known, harbors a dark personal secret: a missing sister of her own. It is her journey to face up to her past that runs through each episode and provides the emotionally charged denouement of the series. Each episode tackles a very different missing person case which MJ and her team must try and solve. They are in a race against time, since each case often involves people at risk, either from themselves or others. The process of investigation is a key element in their journey to find the missing person and also provides dramatic impetus for the viewer. This includes MJ's psychological profiling of the missing person and also the team's tracking and tracing, which requires the use of all manner of modern technology as well as old fashioned police legwork. Whether it is thirty minutes, or thirty years, when someone goes missing, lives are irrevocably changed. Those left behind are plunged into a sense of limbo: not knowing why their loved one has left and worse still, if their loved one is still alive.