Anybody who has never seen the finale of series one has a real treat in store. The rest of us can marvel again at the way writer Mark Gatiss knits a web of brainy plotting that leads to a delicious final reveal at a public swimming pool.
We start with a bored Sherlock (Benedict Cumberbatch) lounging about at 221b Baker Street, absent-mindedly firing a gun at the wall and berating the criminal classes for their inactivity. His brother, shadowy government mandarin Mycroft (Gatiss), wants him to take on a case of national importance.
Then, some explosive developments mark the start of a deductive obstacle course devised by someone very evil for Sherlock to solve against the clock.