As filming on Sherlock series 3 continues in the United Kingdom, today we’re learning the title of episode 2. Even better: It may provide a big clue as to what’s coming in the storyline.

Sherlock series 3, episode 2’s title is “The Sign of Three.” What’s interesting about this title, as noted by The Radio Times, is that it’s a play on Arthur Conan Doyle’s Sherlock novel The Sign of Four, in which Watson meets Mary Morstan. He later marries her.

The role of Mary Morstan for Moffat’s television series was just cast two weeks ago. Who’s playing her? Martin Freeman’s real life partner Amanda Abbington!

This isn’t the first time we’re speculating that a wedding is on the horizon in Sherlock series 3. Creator Steven Moffat revealed three words this past August that were clues pertaining to the plot. One of them was “wedding,” which now appears to connect to Watson and Mary Morstan.

The script for “The Sign of Three” was written by Steve Thompson, who also wrote the series 2 finale “The Reichenbach Fall” as well as “The Blind Banker” in series 1.

Sherlock series 3, episode 1’s title is “The Empty Hearse.” The cast and crew are currently filming the first two episodes of series 3 and will take a break before returning to film the final episode.

Last month we learned that Benedict Cumberbatch and Martin Freeman are already signed on for Sherlock series 4.

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