Prime Video’s upcoming Young Sherlock series has officially welcomed a new cast member to its growing cast, which will be led by Hero Fiennes Tiffin (After Movies, The Woman King). The project hails from Guy Ritchie, who will serve as director and executive producer, after previously directing Robert Downey Jr. and Jude Law in the sequel to Sherlock Holmes: A Game of Shadows.

"It's the action-packed origin story of Sir Arthur Conan Doyle's beloved detective in an explosive reimagining of this iconic character," the logline reads. "At 19, Sherlock Holmes is disgraced, raw, unfiltered and unformed when he finds himself entangled in an Oxford University murder mystery that threatens his freedom. Throwing himself into his very first case with a wild lack of discipline, Sherlock unravels a global conspiracy that will change his life forever."

According to Variety , The Wheel of Time star Dónal Finn has been tapped to play James Moriarty, who was a key character in the original Sherlock Holmes stories. Moriarty is best known as the titular detective's longtime nemesis. The iconic character was previously played by Jared Harris in the 2011 film A Game of Shadows and by Andrew Scott in the Benedict Cumberbatch-led Sherlock series. Dune</em>'s Sharon Duncan-Brewster also played a female version of Moriarty in 2022's Enola Holmes 2.

Young Sherlock Holmes is written and executive produced by showrunner Matthew Parkhill. Finn will also join previously announced cast members Joseph Fiennes as Silas Holmes, Natascha McElhone as Cordelia Holmes, Zine Tseng as Princess Gulun Shou'an and Colin Firth as Sir Bucephalus Hodge. The executive producers are Lane, Simon Kelton, Ivan Atkinson, Simon Maxwell, Dhana Gilbert, Colin Wilson, Marc Resteghini and Harriet Creelman.