The current series of Sherlock only started airing on New Year's Day but next week fans must begin the long, long, long wait for new material. The last episode – ominously titled The Final Problem – airs on BBC1 this Sunday and by all accounts it's a stonker. 

How do we know? Well, we actually saw it on Thursday night, too. But we're keeping schtum on the details for now and focusing on the reaction of the 450 or so people who crammed into the BFI to clap eyes on Benedict Cumberbatch and Martin Freeman's series finale. 

Suffice to say, they were rather blown away by the results. 

As always with Sherlock, the unexpected is expected...

Tweeter @cumberbatchweb hailed it the "best episode of series 4 by far" – and considering the response to last Sunday's The Lying Detective, that's a heck of a claim. 

Sherlockology described tension "so through the roof we're trying to pick ourselves up off the ceiling". 

Expect some serious thrills. 

And make what you will of this very special guest at last night's screening...

The Final Problem airs this Sunday at 9pm on BBC1