Not much longer to wait till “the big day” but here are my predictions for what we might see in tonight’s episode. Let’s start off with titles for this one. Quite clearly a play on The Sign Of Four which is the story where John first meets Mary Morstan. It’s very fitting then, that this is the episode where John and Mary tie the knot.

There weren’t many setlock spoilers for this episode so what we do know is pretty much what everyone knows. Sherlock is the best man (obviously, or perhaps not so obviously to him). He makes a comedic and probably slightly cringeworthy at times best man speech. It wouldn’t surprise me if he started deducing some of the wedding guests and embarrassed John.

Forty minutes into the episode we get less of the comedy and happy wedding drama and more of a traditional case drama as “something” happens at the wedding. Judging from the adverts, it’s a murder (Sherlock will be pleased). Presumably Sherlock will have to solve a crime at the actual wedding reception itself but I’m thinking it will be a little more complicated than an Agatha Christie style whodunnit. Perhaps they have to actually prevent a murder, or prevent a further murder. Obviously John will have to get involved, temporarily putting his wedding celebrations on hold.

Taking into account the episode title and the fact that it involves Mary, one has to wonder whether there will be any aspects of the Sign of Four included. It’s likely that there will be members of Mary’s family seeing her get wed to John, possibly even her father. Maybe he’s the one who gets killed and the murderer is a man with a prosthetic leg. Maybe he gets killed WITH a prosthetic leg. Either way, I think it would be a shame if they didn’t give at least one further nod to the Sign of Four plot.

If the entire episode is set at the wedding, then I’m predicting it will end happily with Sherlock playing the violin whilst John and Mary have their first dance.

It will be interesting to see whether Magnussen comes into it again like he did at the end of last week’s Empty Hearse – we caught a tiny glimpse of him watching the video footage of John’s near BBQing. It’s obvious that this Series involves a Magnussen story arc, but will it be similar to the Moriarty one where he was involved in every episode on some level?

I can’t imagine him making an appearance at the wedding however, and I doubt they’d repeat the idea of him watching on video cameras, but it’s quite possible that the criminal behind the main case (whatever it may be) is in the employment of Magnussen.  We may not even find that out until the final episode so it will probably appear as a standalone case, with Sherlock unaware of the connection.