On 9th February 1983, a grisly discovery alerts Hornsey Police to a serial killer, operating under their noses for years. DCI Peter Jay is stunned when meek Dennis 'Des' Nilsen freely admits to killing multiple men without knowing why.

As the investigation continues, bits and pieces fall into place. Des is interviewed in depth by a writer who is intent on penning a biography of the killer. DCI Peter Jay is frustrated by Scotland Yard's brass. The trial commences.