Sherlock and the two-year cliffhanger

Benedict Cumberbatch as Sherlock Holmes and Martin Freeman as Dr Watson.

It is a mystery that has kept Sherlock fans on tenterhooks for almost two years.

And the cliff-hanger ending to the last series about to be finally explained in the UK, fans of the BBC drama have flooded the internet with theories about how Holmes managed to fake his own death.

The great detective - played by Benedict Cumberbatch - was seen to plunge from the roof of St Bartholomew's Hospital in London to apparent certain death.

However, in the final scene, Holmes was shown observing his own funeral, leaving the riddle of how he could have survived.

The show's eagerly awaited return in Britain this Wednesday is expected to provide a suitably ingenious solution to the mystery that has intrigued viewers since the end of the previous series in January 2012.

Among dozens of unlikely suggestions on social networking sites are that he was 'abducted by aliens' or his fall was 'cushioned by his own ego'. However, five more plausible theories have emerged as favourites. They point out that although the camera angles made it seem Holmes landed on the road, the moment of impact was not shown before the body was found on the street by his sidekick Dr Watson - played by Martin Freeman.

Soon after the last episode, the show's creator Steven Moffatt warned armchair sleuths: "There's a clue everybody's missed. It's not a cheat. We've worked it out. It all makes sense."

And Cumberbatch said: "Sherlock fans won't be disappointed. The explanation is ingenious, witty and generous."

- DAILY MAIL