Nothing has been the same in The Prince's household since he traded one of his fine hunting dogs for a strange, green-jacketed monkey, and now his Kingdom, in Medieval Gwynedd, is starting to suffer. One thousand years later, in modern day Beddgelert, Martyn Llewellyn is struggling to recover from a traumatic childhood and has been offered the chance to make a name for himself at Bangor University through conducting an experiment on dogs. The lives of Martyn, The Prince, and The Prince's son are inextricably linked: haunted by their own demons, their own 'Black Dogs', each has to find a way to survive.