Keep seeing things about how people are having trouble with how disjointed the episode seems to be. And it does jump all over the place an awful lot. But I wonder if that isn’t a little bit intentional.
Do you think any of these characters are feeling any coherency in their lives just now? They’re all spinning in circles, trying to reconfigure their lives and find some solid ground to stand on. Everybody’s following a different emotional trajectory. So each time the scene switches and the mix of characters changes, it feels like the episode is suddenly going in a totally different direction.
Sherlock himself is the primary culprit here. Many people have commented on his apparent instability. And he absolutely is acting erratic. But part of that is because because Sherlock is following two separate emotional arcs at the same time.
The first is fitting back into his old life. He tells Mycroft he needs to reground himself in London, and he does. We see him spend time in turn with every important person in his life, up to and including his parents. We see him LITERALLY ground himself in London with all those mind palace map scenes, where he’s got London plastered across him. And when John isn’t in the picture, we see Sherlock grow increasingly comfortable in his place throughout the episode. By the end, when he’s standing in Baker Street he looks perfectly natural there again. The lights are back on, he’s dressed reasonably, things are (relatively) clean and his notes are once again scattered across every surface of the flat.
But when he’s with John, or thinking about John, he’s back in chaos. He’s at such a loss, in a nosedive he can’t seem to pull out of from the moment he faces John and sees what he truly did to him. His legs stay swept out from under him on that count for most of the episode. In the train car, that’s what he’s babbling. He hurt John so badly, he understands now, and he’s absolutely desperate to make it better somehow. “I don’t know how to fix it, I can’t fix things.”
And that really, truly does completely fuck with him. He’s having a hell off a time getting any casework done, because all he can think about when he’s on a case is how John should be there.
And look how utterly terrified he is when John gets kidnapped. All his self-satisfaction and grace under fire completely desert him. Mary is the one keeping her head, cracking the code, thinking to go to Sherlock for help. Sherlock’s contribution is mainly stealing someone’s motorcycle and driving like a terrified maniac. He’s flat-out panicking. He was never like that before when something happened to John. He was concerned, those times, but he had control over himself, because he felt he had control over the situation. Now he’s horrifically aware that he has
absolutely no control over John’s situation anymore, and he’s so afraid that when he pulls up in the motorcycle, he has tears in his eyes.
Sherlock is SO smart, always in control, always able to pull the clues together and work that magic trick and save the day seemingly at the last second. But he’s learning, finally, that you can’t put people back together the way you can take them apart. There’s no magic potion to heal the kind of pain he inflicted—on dozens if not hundreds of people through his life that he didn’t care about (let’s not forget about all the witnesses and total strangers he’s carelessly traumatized over the years), but now, at last, on the one person whose suffering truly matters to him.