Young Sherlock Season 1 Ending Explained: Holmes Family Twist

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James Moriarty, Cordelia Holmes, and Sherlock in Young Sherlock

Published Mar 4, 2026, 10:00 AM EST

Warning: SPOILERS ahead for Young Sherlock Season 1! Sherlock Holmes is going to have to seek some expert counsel after that shock Young Sherlock ending.

While the tragic death of Sherlock's younger sister, Beatrice [Neve Gordon], who passed away as a child after an accident, has resulted in a deep grief that has defined the emotional landscape for both Sherlock [ Hero Fiennes Tiffin] and his brother Mycroft [ Max Irons] throughout the Guy Ritchie-directed series, the big twist at the end of season 1 provides both hope and confusion for the young detective.

In an interview with ScreenRant's Liam Crowley for Amazon Prime's Young Sherlock, Fiennes Tiffin shared his reaction to the big reveal that Beatrice is not in fact dead, as well as his take on his father, Silas' [ Joseph Fiennes] big "turn" for the worst.

Hero Fiennes Tiffin: Bro, he is going to need a lot of therapy to get through what's happened to him there, isn't he? I hate Silas so much. He's beyond horrible. I think if anyone can recover from it, it's Sherlock, but I just think that the writing behind that, storyline-wise, is just so brilliant. And as you say, he just doesn't catch a break, does he? To have that revelation, and then have what happens next with Silas. Yeah, he's going to need a lot of therapy. It's going to be tough to recover from that.

Another relationship that takes a turn to the "dark side" is the one between Holmes and his friend and right-hand man, James Moriarty, played by Dónal Finn. Speaking to ScreenRant about the tension brewing between the pair at the end of season 1, Finn said he found their disaster-ending friendship "compelling."

Dónal Finn: Oh, the dark side... I mean, the fun thing about playing this character, and about any character that we can weigh up their morality, is that they don't believe that it's the dark side. You know what I mean? And I think, particularly in this, it just feels it's like an alternative way of seeing the world, and neither is good nor bad, but just different. And so I think it allowed me to keep playing the character without judgment. And I think what's more compelling up to that point, is the idea for fans of Sherlock, is that what if he was just a great friend, and he would put his neck on the line for this guy, just like in Titanic, because you know how it's going to end — that ends up in a disaster. The idea that they put themselves out there for that other person.

Those that know the Sherlock Holmes lore know that Holmes and Moriarty spend more time as enemies than they do friends, but it's the depiction of their friendship in Young Sherlock, one that's not been explored as much in other Sherlock Holmes adaptations, that makes their turn to frenemies that much more emotional.

Dónal Finn: They value their intellectual capacity, and that's why this becomes such a strong friendship. So they don't find a connection with everyone, but the idea that, because they find this connection, and then it becomes kind of like they let that other person into their vulnerabilities, their insecurities, that they get close, turning that into a rift makes the betrayal so much more emotionally charged whenever that divide between these characters come.

And though much of the blame is placed on Moriarty, Finn told ScreenRant he "tried his best" to think of the character as more of "an alternative hypothesis to a brilliant mind, rather than any kind of villain."

Season 1's ending also opens the door for the introduction of Dr. Watson, and while showrunner Matthew Parkhill said bringing Watson into the fold would "complicate" the series, for Finn and Fiennes Tiffin, it's a "heated rivalry" they wouldn't mind seeing play out.

Hero Fiennes Tiffin: We kind of explored and discussed that, and we feel like it would be really interesting. I don't put it past Matthew to facilitate that without bringing our version of the story to an end. But if the start of [Arthur] Conan Doyle's work begins with Sherlock meeting Watson, I wonder if we have to wait till the very end to do that, because that might kind of wrap up our chapter of the story. As I say, I don't put it past Matthew to find a way to introduce Watson without wrapping it all up, but I don't know. I wonder if we're getting into the territory of needing to draw a line through the word "Young," and it just becoming, "Sherlock," at that point.

Again calling it "interesting," Fiennes Tiffin said he wouldn't "put it past" Parkhill to make it work should the show get greenlit for a second season.

All eight episodes of Young Sherlock, which also stars Zine Tseng, Natascha McElhone, and Colin Firth, are streaming now on Prime Video.