OK so we're in the fictional universe where Sherlock Holmes and Doctor Watson exist but we're 300 years in the future.
Time travel is made possible by harnessing the power of dark matter and the intrepid British team of time travellers Carruthers, Fortescue, Blenkinsop and Fakename travel back in time to before the incident of Holmes and Moriarty at the Reichenbach Falls.
Carruthers, Fortescue and Blenkinsop place tiny microphones and cameras in hidden locations around the Falls while Fakename tinkers with the quantum entanglement matrix on the dark matter drive.
When all is ready they wait far away, in the pub.
Later they return and collect their equipment. Then they return to their own century to examine the recordings.
As they watch the footage they are amazed to see Holmes putting on a disguise, talking to empty air, changing his position, removing the disguise, talking to empty air again, then changing his position and repeating the performance. Each time Holmes repeats the cycle of disguise on, change position, disguise off, change position he seems to become more agitated. He argues with himself, rants and cajoles. He even makes punching and kicking gestures at an imaginary opponent.
Finally, to the intrepid four's aghast gaze Holmes grips himself around the throat and, disguise half on and half off, plunges over the Reichenbach Falls to almost certain death below.
Carruthers, Fortescue, Blenkinsop and Fakename stare at each other in shock.
Voicing the thoughts now resounding through the brains of all four of them Fakename declares, 'Well I never. So that's who Professor Moriarty really was.'
'But,' objects Fortescue, 'Didn't Holmes meet Moriarty in front of witnesses?'
'He did.' responds Carruthers, 'But he could could've hypnotised an actor to do it.'
'But why?' asks Blenkinsop, 'Why would he become his own nemesis?'
'I suppose,' suggests Fakename, 'No-one else was up to the job...'