Somebody kidnaps Sherlock, cuts him open, puts a bomb into him and sews him shut (whether he's unconscious or horrifyingly aware is up to a filler).

Later John is the one who has to remove the bomb out of Sherlock when it's about to explode. He has no time and drugs to make it painless, so... well, it's a nightmare.

Still, John saves Sherlock and the bomb doesn't kill him.

A lot of care and comfort afterwards, please.