Examining one of the most baffling unexplained deaths of recent years. In August 2010, Gareth Williams, a GCHQ employee on a 3-year secondment to MI6, was found dead inside a padlocked duffle bag in the bath of his London flat.

On the night of June 8, 1996, 25-year-old Melanie Hall was enjoying an evening out with her boyfriend in a nightclub. Thirteen years later, her remains were discovered on a slip road off the M5. In October 2019 police revealed they had new evidence, when they obtained a partial DNA profile from the rope wrapped around the bag containing Melanie's remains. Yet still, her killer remains at large. This documentary re-examines the case and explores the theories surrounding her death.