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

As the police continue to question Des on his crimes, forces from on high threaten to bring their case to a premature close. Meanwhile, biographer Brian Masters seeks to analyse why Des did what he did, beginning a dangerous dance with a killer.

As the trial approaches, Jay and Brian reflect on their involvement in the investigation and the impact they've had on Des, realising that regardless of their influence everything will be decided, as it always is, by a jury.