The story of the hunt for murderer Malcolm Webster, who targetted wealthy women for their money. The programme explores the crimes from the perspective of detective Charles Henry, who was behind the three-year investigation to re-open a cold case. He would later be joined by 20 colleagues, who gathered more than 1000 witness statements and used 90 search warrants for banks, building societies and solicitors.

Webster attempts to kill his second wife in similar circumstances to his first wife's death over a decade before. As Webster targets his third victim, a wealthy nurse whom he plans to bigamously marry, time is running out for the investigating officers as they learn that the bride and groom will be honeymooning aboard a yacht sailing into international water.