‘Young Sherlock’: Why Guy Ritchie’s Prime Video Series Isn’t a Prequel to the Robert Downey Jr. Movies

“Young Sherlock” has arrived, marking a Holmes-coming for Guy Ritchie after he gave fans two beloved Sherlock Holmes movies. But don’t get it twisted, Prime Video’s new series is not a prequel to the films starring Robert Downey Jr. — in fact, Ritchie and his team worked hard to make sure it stood on its own.

Now streaming, the series follows a 19-year-old Sherlock Holmes, played by Hero Fiennes Tiffin. At this point in his life, Holmes isn’t a great detective, he’s just a college-age...