Benedict Cumberbatch is back as Sherlock Holmes in a "Christmas special", The Abominable Bride. But it's not Sherlock as you know it - in this episode, Holmes and Watson (Martin Freeman) have been plonked back in Arthur Conan Doyle's original 19th century setting.
After a brief introduction to the characters in this new era (well, old), we're plunged into the mystery: a woman is seen to die on a busy street, yet later that day, she kills her husband.
But Holmes soon loses interest in the case - until several months later when it seems that the dead woman may be threatening the life of an important man.
And then two-thirds of the way through comes the massive, shocking twist that will leave you gaping unattractively.
The episode is full of self-referential jokes, and tidbits that only super-fans would recognise - even the title comes from a throwaway line in a Conan Doyle story. While it doesn't quite fit into the Sherlock canon, if you're a fan, you'll rejoice at the writers' sheer audacity and creativity. Be sure to stay after the credits!
Contains disturbing scenes