Like all great mysteries, this begins with a corpse, five in fact.
This particular case has remained undisclosed for almost three decades. Sworn to secrecy, never to divulge the truth while the living were still at risk of reprisals. I've refrained from publishing or even speaking of those Regent's Park murders.
It's only safe to do so now due to the fact that those involved are either dead or never to be found again.
It remains one of the most astonishing moments in Holmes' career and exposes a shocking revelation about his character.