A case goes badly and John gets seriously injured. It can be temporary or permanent, but we're talking serious with long time rehabilitation. It prompts Sherlock into slowing down. He takes less cases, he takes more file-only cases, he'll only go out on cases with John if they're relatively safe, if they're as dangerous as their usual cases, he'll go alone. He thinks he's doing the right thing, because he'll do anything to keep John safe and alive.

But it just makes John feel useless. From his point of view, if he can't go out on cases with Sherlock anymore, then Sherlock has no need of him anymore. His rehabilitation is slow, and he hates it, and he can feel his friendship with Sherlock falling apart around him as he's recovering.

There's parallels to his life in the army and he's not sure he could take being invalided out of everything he knows and loves again.

Gen or build up, please.