Anyone who has read the Canon — as Arthur Conan Doyle’s Sherlock Holmes stories are known — knows the significance of Reichenbach Falls.

It was there, at the famous Swiss waterfall, that Conan Doyle’s famous consulting detective met his end. In the 1893 story “The Final Problem,” Conan Doyle — sick to death of the notoriety and fame and, yes, stereotyping and literary ghetto-izing that the Holmes stories had placed on his shoulders — decided to kill off Holmes once and for all. (Reader demand led Conan Doyle to reverse the decision a few years later.)

Holmes pursued Moriarty, the criminal genius, the spider at the center of the web of crime for all of England and a good portion of the globe, to the falls. Holmes’ friend and biographer, John Watson, becomes separated from the detective and later finds a note from Holmes. He is about to grapple with Moriarty atop the falls.

Two sets of footprints ascend to the top. No footprints are seen coming back down. Even an amateur detective like Watson can see that.

Tonight’s episode of “Sherlock,” “The Reichenbach Fall,” plays on that theme. After a cat-and-mouse game in previous episodes of the first and second seasons of the BBC series — airing on Masterpiece Mystery stateside — Moriarty begins an all-out assault on Holmes in this story.

Moriarty pulls off three seemingly impossible crimes: He opens the vault of the Bank of England, unlocks the gates of an impenetrable prison and seizes the Crown Jewels from the Tower of London.

But instead of making off with the priceless baubles, Moriarty sits on the throne, be-crowned-and-sceptered, waiting for Lestrade and the other London coppers to arrive.

Holmes testifies at Moriarty’s trial and — being Holmes — irritates the members of the jury so much that they exonerate the criminal. Or is some other game afoot?

After the trial, Moriarty shows up at 221B Baker Street and begins “playing” with Holmes. It is a game that sees Holmes trying to find a computer code of Moriarty’s design that can unlock virtually any door, any secret, a code that makes Holmes a target of an international set of assassins.

Meanwhile, Moriarty begins chipping away at Holmes’ reputation until only Watson is still in his corner. And even Watson’s faith is a little shaken.

Although there are only three “Sherlock” episodes per season — maybe because there are only three — the series is uniformly high in quality and clever beyond compare. I’m guessing they’ll do more episodes this year and we’ll get to see them in 2013. I sure hope so.

Other thoughts about tonight’s episode:

I love the way the series plays with how Sherlock and Watson are perceived. Tonight Watson is irritated to see himself described in the press as a “confirmed bachelor” and constant companion to Holmes.

As a member of the press, I’m a little chagrinned about how it was portrayed tonight. But it is the British press, after all.

Benedict Cumberbatch and Martin Freeman continue to be among my favorite Holmes and Watsons of all time. Cumberbatch in particular isn’t afraid to play Holmes as unlikable for most of an episode.

Andrew Scott played Moriarty with just enough crazy. A little bit more would have been too much. If tonight’s episode, in the style of “The Final Problem,” proves to be his swan song, it was a good one.

Most of this show is attention-grabbing and attention-keeping. There’s some effort involved, of course, in keeping up with the quick-paced, accent-tinged dialogue delivery. But the riveting stories and scenes are another reason to keep watching the screen. The two main dialogue scenes between Holmes and Moriarty in tonight’s episode could not have been more mesmerizing.