The BBC series Sherlock episode about Sherlock’s wedding best-man speech is “The Sign of Three.”
The episode centres on John Watson’s wedding to Mary Morstan and Sherlock’s role as John’s best man. Sherlock struggles with the social expectations of the speech, while clues hidden within wedding memories lead him to investigate a possible threat. The title combines the wedding’s central trio with a reference to the Holmes story “The Sign of the Four.”
“The Sign of Three” was written by Mark Gatiss, Steven Moffat and Stephen Thompson, and directed by Colm McCarthy. It is the second episode of series 3 and aired in January 2014. Martin Freeman’s real-life partner at the time, Amanda Abbington, played Mary Morstan.
The episode is sometimes confused with “His Last Vow,” which is the series 3 finale. “The Empty Hearse” opens the series, while “The Sign of Three” is specifically the wedding episode.