Is This The Final Series Of BBC’s SHERLOCK?

And will the next three episodes step outside of the canon?

BBC's Sherlock is the best version of the character in decades, and the show's popularity has launched Benedict Cumberbatch into a whole new world of stardom. But that world makes it hard to find time to shoot the program, and there have been recent rumblings that the third series of three movies will be the last. Those rumblings have been given some support by three words spoken by showrunner Stephen Moffat at the Edinburgh TV Festival today:

Rat, Wedding, Bow.

These were his hints as to what series three would adapt, and 'Bow' is the word that makes us think this is the finale. His Last Bow is the final canon Holmes story - chronologically, not in terms of publication. Set in 1914, it finds Holmes and Watson retired from detective work (Holmes now keeps bees in the country and is working on a book about investigation) but not from intrigue. The duo have been busting a German spyring in the days just before WWI. The story was published in 1917 as a pretty blatant piece of propaganda; I'm curious how this story would be adapted for the show. Would the final episode flashforward some years to find Holmes and Watson older and mixed up with Mycroft's spying?

His Last Bow is also notable for being the only Holmes story told in third person, ie, not narrated by John Watson. As a series finale this opens the possibility of a different structure for the episode.

"Wedding" seems to likely indicate The Noble Bachelor, which has a missing bride who disappears at the reception after her wedding. 

It's "Rat" that intrigues me. There's a famous rat in Holmes' canon - the Giant Rat of Sumatra. But there is no story of the Rat*; rather, in The Adventure of the Sussex Vampire Holmes remarks to Watson: 

Matilda Briggs was not the name of a young woman, Watson, ... It was a ship which is associated with the giant rat of Sumatra, a story for which the world is not yet prepared.

There have been dozens of fanfic attempts to tell the tale of the giant rat, but there is no canonical story from Sir Arthur Conan Doyle about it. So is Moffat and his team preparing to indulge in the time-honored tradition of adding to the canon? Many great authors and filmmakers have done just that (Nicholas Meyer, director of Star Trek II: The Wrath of Khan, wrote probably the very best of them all, The Seven Percent Solution), so it would be exciting to see Moffat's show - which has already taken major liberties - do just that.

* beware any website telling you that the show is adapting The Giant Rat of Sumatra, which is the title of a bunch of faux-Holmes novels, the latest of which came out in 2010. These sites did not do their research.