At this stage, it’s easy to take for granted just how strong the casting and performances are in Sherlock, but it would be a disservice to do so. Benedict Cumberbatch and Martin Freeman are every inch Sherlock and John in The Empty Hearse, as if they’ve been kept in costume and in storage for the last two years instead of out and about headlining Hollywood’s biggest releases. Even in this, the week The Hobbit sequel is released, all Freeman has to do is stand in front of Sherlock’s gravestone, and it’s Bilbo who? Cumberbatch has only to put on that coat, and his beefier Star Trek Into Darkness counterpart evaporates.

If the stars are clearly comfortable in their roles, then the writing is luxuriating. It’s also cheekier than ever. Rather than ignore the success of the series, The Empty Hearse absorbs its own celebrity and serves it back to the audience as winks and fan-pleasing references. Some will call that self-indulgent but it’s all so winningly handled that it provides the gentle warmth of being in on a joke instead of the lurid glare of an ego-trip. Besides, who can begrudge a little indulgence when it makes so many people so happy? Certainly not us.

The variety packed in to the ninety minutes is both a boon – the thing moves along at a fair whack, at no point dips in energy – and a potential weakness. With more catching up, regrouping and track-laying to do than most episodes of Sherlock, there’s a sense perhaps that The Empty Hearse is a succession of good bits rather than a complete story. Highly enjoyable, cleverly constructed good bits it must be said (when the cast were asked to name their favourite scenes in the post-screening Q&A, there were so many to choose between that each one mentioned nudges you to think ‘Oh yeah, wasn’t that good?’), but a compilation all the same.

A couple of elements may have contributed to that sense, the first being that The Empty Hearse sets up some mysteries to be solved in later episodes. A shadowy threat drives the action-thriller side of things, and it’s far too early for that villain to fully show their hand. The episode’s most important parts – its relationships and emotional stories – are affectingly realised, but there’s a to-be-continued when it comes to the action.

The Empty Hearse is also one of Sherlock’s most stylised episodes yet. Director Jeremy Lovering takes the visual flair established by Paul McGuigan in the first and second series, and ratchets it up a notch, visually chopping up an already scattered story. In addition to the now-characteristic floating text, there are sections here that have the standalone feel of a music video, or – appreciating the enormous differences in budget – a Bourne or Bond-style action movie. The stunts and special effects are bigger than anything we’ve seen before from Sherlock. Suffice to say that the episode felt entirely at home in a cinema.