Written by Lauren Shultz and Christian Bone

After Moftiss casually dropped the bombshell at the end of ‘His Last Vow’ about Sherlock and Mycroft having another brother, fans have gone crazy speculating on who this mysterious new character would be and what happened to him. In last week’s ‘The Lying Detective’, we shockingly found out that their secret sibling is in fact a sister – and she’s evil!

But is that all that there is to it? Or is there a fourth Holmes sibling? In the aforementioned episode, Sherlock mentions that people like to stop after three – is that a sneaky hint by Moffat that the third brother is still out there, to be revealed in the season finale ‘The Final Problem?’

Let’s have a look at who they could be…

6. Wiggins

One of the most popular theories that had been going around before Series Four aired is that Bill Wiggins is somehow related to the Holmes boys. This would explain his immaculate deduction skills. However, there are several problems with this theory. Firstly, his name is Bill, which is short for William. That’s Sherlock’s first name. His parents would never give their children the same name. Secondly, Mrs. Holmes obviously didn’t recognize him when Sherlock brought him over for Christmas. Also, Wiggins is canon in the original Conan Doyle stories: a teenage boy in charge of “The Baker Street Irregulars”, the equivalent of Sherlock’s homeless network. With that being said, it is highly unlikely that Wiggins is somehow related to Sherlock and Mycroft.

5. An Institution

In both ‘The Six Thatchers’ and ‘The Lying Detective’, Mycroft mentions the name Sherrinford. Fans will know that this is the name given to the third Holmes brother in various novels by Sherlock Holmes writer. However, what if this choice of name was deliberately made to fool fans.

The phrases he uses are “Put me through to Sherrinford” when on the phone, and he tells Lady Smallwood that he gets “regular updates” from Sherrinford. Neither of these is necessarily referring to a person. It could be that Sherrinford was the name of the institution that Euros was being kept in until she recently escaped, unbeknownst to Mycroft.

4. The False Accusation

This is my personal favorite. The basis for this theory is how much Sherlock despises Mycroft and that there has to be a logical reason for it. It could be because Mycroft is overprotective of Sherlock and he just comes across as extremely annoying in Sherlock’s mind, but I don’t think that’s the whole story. Why would Mycroft be so protective of him anyway, especially now that Sherlock has John? It’s because Mycroft is responsible for what happened to the other brother.

Mycroft says in ‘HLV’ that he’s not overly compassionate when it comes to family, because “you know what happened to the other one”, meaning the other brother must have done something, or at least been accused of something, very serious and Mycroft did not intervene. As a result, the other brother was imprisoned and either got sick or was attacked and died. With Mycroft’s power in the government, he could have easily gotten his brother off, but he didn’t, which means that he believed he was guilty. But Sherlock didn’t. He thought he was innocent, which is why he blames Mycroft for being entirely responsible for his death. Now Mycroft is trying to be overprotective of Sherlock because he knows he made a mistake, but Sherlock is still angry and doesn’t want anything to do with him. That would also explain why Sherlock started drugs. In my opinion, this is a very plausible theory, but we’ll have to wait to see how the story plays out.

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