Benedict Cumberbatch returns as Sherlock. BBC One

It's the smash hit TV drama whose leads have gone on to conquer Hollywood, but on New Year's Day, after an agonisingly long two year absence, Sherlock will return. The last time we saw Benedict Cumberbatch's genius detective, he was flinging himself off the roof of Saint Bartholomew's Hospital in what appeared a necessary suicide in order to save the lives of his friends.

Because of the show's phenomenal success both in the UK and around the world, it was always going to be a question of how, not if, Sherlock survived, but the mystery of his death-defying plunge remains. Here are a few theories as to how the great detective faked his own death.

The Refuse Truck

To provide a recap. The Season two final, The Reichenbach Fall, saw Sherlock confront his nemesis Moriarty on the roof of Saint Bartholomew's Hospital, where he was informed that unless he committed suicide the three people closest to him, John Watson, Mrs Hudson and Lestrade, would all be gunned down by assassins. Moriarty then kills himself to stop any chance of his true identity being revealed, leaving Sherlock with no choice but to take that fateful step over the ledge and plunge to his death.

One possible explanation is that Sherlock really did jump off the building, but something broke his fall . As passers-by clamber around the corpse, we see an open-top refuse truck moving down the street, one that could easily be arranged by Mycroft as a means to ensure the bin bags provided a soft landing for his brother. Sherlock could then have got creative with fake blood and pretended to be dead, or a corpse resembling Sherlock could have placed on the pavement from the same truck to make it look like the great detective was dead.

Counting on Molly Hooper

But wouldn't John witness the ruse? As he rushes over to the body he is knocked over by a passing cyclist, once again an incident that could easily have been orchestrated by either Mycroft or Sherlock's homeless network. Watson appears in a stupor afterwards, which you might expect if you were hit by a bike, but it could also be that the cyclist unleashed the secret army gas from previous episode 'The Hounds of Baskerville', in order to daze John and enhance the fear and paranoia that he had just seen his best friend die.

Sherlock returns in new episode The Empty Hearse on New Year\'s Day. BBC One

But even if Watson was made sure the fall was genuine, how would the police, paramedics and morticians be convinced that it actually was him who died? This is where Sherlock's ally Molly Hooper comes in. The coroner was frequently exploited by Sherlock throughout the show, but in their last conversation, the cold-hearted sleuth opened up by telling her she does count and that he trusted her. Moriarty recognised the importance of Sherlock's friends John, Mrs Hudson and Lestrade by threatening their deaths, but did he in fact miss out on his most important colleague, one who could easily provide a cadaver and claim the body that arrived in the morgue to be Sherlock?

How to Disappear Completely

Sherlock did not return after cheating death, but disappeared for two years. How did he remain undetected without Moriarty's people finding him? Once again Mycroft's secret service connections could provide a solution. Or perhaps Janus Cabs are involved; the shady company uncovered by Sherlock in series one episode 'The Great Game' that specialised in helping people disappear when they're in a tight spot?

Maybe some, or none of these theories actually happened, and a solution that was missed will be unveiled. Whilst we don't know if how he faked his death will be revealed, we do know that Sherlock will return in brand new episode "The Empty Hearse" for three more action packed adventures at the start of the New Year.

The new series of Sherlock returns to BBC One at 9pm on New Year's Day.