Sherlock Season 4 Finale: 13 Dumbest Moments From 'The Final Problem'
6. Everything On The Plane
The episode started not with Sherlock and Watson, or even Eurus, but a young girl waking on a plane, discovering everyone else was unconscious, and she was headed towards disaster.
From there, this strand of the story gave Sherlock, Watson, and Mycroft impetus, the main problem they had to solve. It was often distracting from the more centralised elements anyway, but then it was revealed that - woah! - there was no girl on the plane.
Instead, it was Eurus all along, pretending to be the child, effective her own version of a 'mind palace' - a way of visualising her mental state. It just, well, didn't really make any sense. From her mimicking the girl to phoning herself with the voice of Moriarty, right down to its resolution, which was that she needed a hug from the brother she'd long wanted to kill.