As I’ve mentioned before, Holmes fans were obsessing over continuity, inconsistency and details years before it became common for Trek, comics and other fandoms. And few things have inspired as much speculation as Holmes’ return in The Adventure of the Empty House.
As Holmes explains it to Watson, he faked his own death so that he could work secretly to entrap Moriarty’s remaining lieutenants, most notably ex-army officer and celebrated big-game hunter Col. Sebastian Moran. He spent the two years traveling in Tibert (under the pseudonym Sigerson), Persia, Mecca and researching “coal tar derivatives.” When Holmes deduces the murder of Ronald Adair — apparently shot at close range in an empty room — is Moran’s work, he returns to London to take the villain down.
The trouble is, Moran ambushed Holmes at Reichenbach in the moments after Moriarty falls to his death. It’s understandable lying low made more sense after that than Holmes returning publicly to London (Moran’s a crack shot), but why lie to Watson? If Moran already knew Holmes was alive, there’s no need for Watson to give a convincing show of grief. So what’s the real story?
One school of thought is that despite inconsistencies in Holmes’ account (there are practical problems with his course of travel that I won’t get into here), we should accept the story at face value: Holmes was away, he did have those explorations, case closed.
Another view is that he spent the two years working in London to take Moran and the other survivors of the Moriarty ring down. Watson knew this but didn’t want to admit it so Final Problem and Empty House offer an alternative sequence of events where Watson had no idea he was giving his readers a false yarn.
A popular view with romantics is that Holmes was away but not on the trip he told Watson (or that Watson offered to the public). He was in the U.S. working on various cases. He was acting as a secret agent for British interests, as he does later in His Last Bow. He spent at least part of the time on a romantic idyll withIrene Adler; there’s a school of thought that their child (depicted in Sherlock Holmes in New York) grew up to be fictional detective Nero Wolfe (all rights to image remain with current holder).
Then there are the wilder theories. Seven Percent Solution is built around the idea that Moriarty was a fantasy from Holmes’ cocaine-addled brain and that his time away involved clearing his head and kicking the drug habit. An earlier variation on the idea is that Holmes simply made up Moriarty to explain away some of his failures.
Other theories suggest that Holmes did, in fact, die at Reichenbach. Watson knew he could generate some extra money writing more Holmes stories, so he mixed real cases with made up ones. Or it was Moriarty, not Holmes who survived The Final Problem, and took his old foe’s place (a twist on this in one Wild, Wild West episode has a Holmes analog posing as Moriarty to give himself entertaining crimes to solve).
I don’t have a strong opinion on this myself, other than yes, Holmes would have told Watson he lived a lot sooner. Beyond that, the truth is anyone’s guess.