The new Prime Video series Young Sherlock is now streaming, and it brings a major change to the Sherlock Holmes story. The show, directed by Guy Ritchie, imagines what happened when the world’s greatest detective was just 19 years old. But the biggest twist involves his future archrival, James Moriarty. In this version, they start as close friends .
The series premiered on March 4, 2026, and all eight episodes are available to watch now . Hero Fiennes Tiffin plays a young, rebellious Sherlock, while Dónal Finn takes on the role of a charismatic James Moriarty .
A Friendship That Changes Everything
In Young Sherlock, the famous enemies meet at Oxford University in the 1870s. Sherlock is not the polished detective fans know. He is described as “disgraced, raw, unfiltered, and unformed” . He lands at Oxford after getting into trouble, working as a janitor-like porter.
That is where he meets Moriarty. Unlike other students, Moriarty sees Sherlock’s brilliance right away. Dónal Finn, who plays Moriarty, says the two characters immediately recognize something in each other. “They’re both outsiders,” Finn explained in an interview. “They both probably feel a little bit like outsiders. When they meet each other at university, they recognise something in each other that’s possibly rebellious towards the people they find themselves surrounded by” .
Showrunner Matthew Parkhill wanted to explore why these two became such important rivals. He said, “What if they knew each other? What if it were like a great Butch and Sundance friendship that turned bad?” . This idea makes their future conflict much more personal. Every fight they have later will feel like a betrayal because they were once brothers in arms .
Moriarty’s Personality and Irish Roots
This version of Moriarty is different from any seen before. He is charming, clever, and funny. Dónal Finn gives the character a distinct personality by using a Kerry accent . He based the voice on old-school Irish storytellers, or seanchaithe. Finn explained, “Moriarty is able to hold people’s attention in such an amazing way, and that’s how the seanchaithe worked as well. They were incredible storytellers” .
In the show, Moriarty is an Irish student on a scholarship at Oxford. He has to work harder to fit in. Finn described him as someone with “a chip on his shoulder” who has “something to prove” . This makes him a sympathetic character, not a villain. At this point in his life, he is just a realist. He tells Sherlock early on that “the world is unfair, people can be unkind” . There is no evil plan yet, only a young man trying to survive in a world stacked against him.
How They Work as a Team
The chemistry between Hero Fiennes Tiffin and Dónal Finn is a highlight of the series. Reviews note that their relationship is the most interesting part of the show . The two actors worked hard to build that connection.
Fiennes Tiffin shared that they practiced scenes to make their characters feel in sync. “We worked a lot of scenes in prep, making sure that we kind of finish each other’s sentences or we sip our drink at the same time, stand up at the same time, sit down at the same time” . This synchronicity shows viewers why these two would be friends. They operate on the same wavelength .
In the story, they get pulled into a murder mystery together. Sherlock is framed, and Moriarty helps him clear his name . Their adventure takes them across the globe, from London to Constantinople . They face danger together, and Moriarty even helps Sherlock learn to handle himself in a fight .
Not Evil Yet, But Hints of What’s Coming
For fans who know the original stories, watching their friendship is bittersweet. Moriarty is not evil in Season 1. Matthew Parkhill made sure not to rewrite anything from Arthur Conan Doyle’s books. Instead, he filled in the gaps. “I can’t re-write anything of Conan Doyle,” Parkhill said. The show invents the emotional backstory that the books never covered .
But there are small hints. Dónal Finn plays Moriarty with a “twinkle in his eye which sells the character’s mischief and inner darkness, even as he is outwardly all justice and light” . Audiences will spend the whole season waiting for the other shoe to drop, wondering when this friendship will break .
Reviews suggest the show handles this tension well. The “friends to foes” angle plays out with “surprising subtlety” . The series ends without resolving their relationship, leaving room for future seasons to explore how Moriarty transforms into the “Napoleon of Crime”.
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Cast and Where to Watch
Besides the two leads, Young Sherlock features a strong British cast. Colin Firth plays Sir Bucephalus Hodge, a university dean . Joseph Fiennes (real-life uncle to Hero) plays Sherlock’s father Silas, and Natascha McElhone plays his mother Cordelia . Max Irons appears as Sherlock’s brother, Mycroft .
You can stream Young Sherlock exclusively on Amazon Prime Video. The platform released the full first season on March 4, 2026 .
If you enjoy fresh takes on classic characters, this series offers a thrilling adventure that reimagines the early days of literature’s most famous detective.
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