Like his colleagues, he is allowed only to expand on the most uncontroversial Sherlockian topics. A fourth season is coming (“I’ve said we’ll go into production on it in a year, not any specific year,” Gatiss has said) and Cumberbatch deploys his most diplomatic smile when quizzed on how this slice of Victoriana ties into the show’s present-day setting – or how it resolves the desperate cliffhanger at the end of the last season. “Nice try, nice try,” he mutters wryly, conceding only that while the trip into the 19th century “is a great deal of fun, it does advance things. It’s not just on its own.”