But if you just can't wait until Sunday, Digital Spy has picked out ten teasers and quotes from the episode to tide you over.
WARNING: The below hints are deliberately vague and free of concrete spoilers, but for anyone who wants to know absolutely nothing about 'The Sign of Three', turn back now!
1) The core of the episode is one extraordinarily long monologue: Sherlock's best man speech is interwoven around extended flashbacks, which fill in chunks of the six-month gap between 'The Empty Hearse' and the wedding day.
2) Sherlock has more than a few surprising extracurricular skills up his sleeve. One is napkin origami. Another recalls one of Moffat's best-loved episodes of Doctor Who.
3) "Either I've caught you in a compromising position, or you're working out again."
4) Remember Mrs Hudson's husband who was executed for double murder? We find out quite a bit more about him.
5) John's stag night is the funniest sequence in the show's history.
6) "Yeah, but am I a pretty lady?"
7) The whole episode is essentially a love letter to John Watson.
8) A very familiar face from Sherlock's past makes a brief but rather thrilling return.
9) "Oh, Sherlock. Neither of us were the first, you know."
10) By the end of the episode, we find out what Sherlock's "last vow" is.
'The Sign of Three' will air on BBC One on Sunday, January 5, followed by 'His Last Vow' on January 12.
Gallery - Sherlock series 3: