As Sherlock fans will know, each series of the show is teased before hand by three key words chosen by Moffat and Gatiss. For Series Two, for example, these words were Woman, Hound and Fall. This turned out to refer to the presence of Irene Adler, the Baskerville Hound and Sherlock’s fall from St Barts. Now, thanks to the Sherlock panel at San Diego Comic-Con, we have the three key words for Series Four. So what are they?

Interestingly, the words are all names this time around. And those names are: Thatcher, Smith and Sherrinford.

Certain Sherlockians might already be jumping up and down at one of those names but, before we join them, let’s look at the potential meaning behind these words.

1. Thatcher

This one is the most head-scratching to try and deduce. Usually these words are pulled from something from the Conan Doyle stories, but Thatcher is not a name that turns up in the original Holmes canon. Instead, it has appeared in Sherlock itself.

For most people, the name Thatcher conjures up former British Prime Minister Margaret Thatcher. Thatcher was referenced in Series Two episode ‘The Hounds of Baskerville’ as a hero of Major Barrymore’s. Could this be what Mofftiss are referring to by choosing that word? Is the Major making a, erm, major comeback in Series Four?

Margaret Thatcher was also referenced in ‘The Six Thatchers’, an account of a case on John Watson’s blog (an official tie-in to the show). The case is based on Doyle story ‘The Six Napoleons’, which is one that the series has not yet adapted. Did Moftiss like the blog post so much they decided to make it a proper episode? Could be.

2. Smith

This is a much easier one to answer. Beware, though, we will be discussing things that the BBC might not want you to know yet, so you may want to look away now.

Thanks to an online CV, we know that Toby Jones is playing Culverton Smith in Series Four’s second episode. Smith was the villain of Doyle’s ‘The Dying Detective’, in which the character is a fiendish poisoner. Jones’ version seems quite different from the original, though – we got our first glimpse of him in the new trailer.

Jones previously described his character as an incredibly “dreadful” person, so expect his villain to outrank Magnussen in the despicable stakes.

3. Sherrinford

Oho, this is the big one. Of all these words, this is one that will get fans’ hearts racing. Why is that? Because Sherrinford is none other than the other brother of Sherlock and Mycroft!

The character is not actually a Conan Doyle creation but rather an invention by Sherlockian scholar William Baring-Gould who invented Sherrinford, based on evidence in the original stories, for his in-depth Sherlock Holmes biography. Holmes Boy No.3 has since appeared in various stories by other writers.

Sherrinford was previously hinted at in ‘His Last Vow’, in which Mycroft said, after mentioning that he is not known for caring for his siblings, “you know what happened to the other one.” Since then, the internet has collectively decided that Tom Hiddleston will appear at some point in the future in the role. After this announcement, that idea suddenly sounds a lot more plausible…

Have these three words whet your appetite for new Sherlock? Does Sherrinford mean what we think it means? Leave your thoughts in the comments!