Sherlock has thrown a bunch of twists at us this season, but the Season 4 finale of Sherlock really pulled out all the stops and delivered some important answers to Holmes family backstory. For years, we've heard about Redbeard, Sherlock's dog who meant a great deal to him and a pet that he lost some time ago. But there's a deeper connection to this story and it begins and ends with a boy named Victor Trevor. So who is Victor Trevor on Sherlock? It turns out that he and Redbeard are actually one in the same.
At the beginning of the episode, our Baker Street boys find themselves at Sherrinford in order to deduce how Eurus Holmes — Mycroft and Sherlock's other sibling — managed to escape to play tricks on them in Episode 2. But as per usual in the Holmes family, Eurus proved to be three steps ahead of everyone else and set up an elaborate game for them to play out. But the final twist came at the end when Sherlock discovers that Eurus hadn't killed his dog Redbeard at all. In fact, it turns out that Sherlock has never had a dog in his life due to their father's severe allergy toward canines. Evidently, his mind had managed to convince itself that the important living thing he'd lost had been a pet because the reality of the situation had been too painful... like the loss of a close best friend.
That's right, folks. Victor Trevor was Sherlock's best friend as a child. In fact, the two of them loved playing pirates together and Victor always pretended to be — you guessed it — Redbeard. So Victor Trevor and Redbeard are actually one in the same, which makes what Eurus did all the more horrifying. You see, Sherlock's sister wanted to play with them as well, but felt extremely excluded from the fun, so she decided to get rid of the competition for Sherlock's attention by allowing Victor to drown in a well. John Watson stumbled across the young boy's remains when he too was trapped in the well by Eurus, almost making history repeat itself in an all-too-cruel way.
Thankfully, as always, Sherlock was able to save the day just in time and not let his current best friend meet his childhood best friend's fate. And now Eurus is safely locked away, unable to hurt anyone ever again. (Hopefully.) But it's still a devastating part of Sherlock's past to discover and perhaps helps us to see how he became the man he is today. Let's just hope the series will eventually get a Season 5 renewal, so we can dive even deeper to the always-intriguing story of Mr. Sherlock Holmes.