As we usually have to wait what feels like 47 years between Sherlock series, there's only one thing that's going to happen: fan theories.

It was bad enough when Sherlock managed to fake his death after a rooftop fall in the second series. Now, we're scratching our heads as to how Moriarty has apparently also returned from the dead. Or has he?

From current mysteries to secret alliances, here are just some of the very best of Sherlock fan theories. Some of which would earn you a Sherlock verbal smackdown for suggesting, while others are actually quite believable.

1. The whole series is just Mycroft keeping Sherlock sane, and John is an actor

BBC

This theory is quite a convoluted one, so strap yourselves in. What if all this time, everything was just a fake-out that Sherlock's enormously powerful big brother is making up? All these crimes and villains are just there so he has something to do, and to keep him off the drugs.

Whenever Sherlock's bored, he turns to drugs. But Mycroft is fully aware of this, so he sets up elaborate crimes for Sherlock to solve. And maybe to help him, he hired an actor named John Watson.

Yes, we know what you're thinking. Utter baloney. But when Sherlock first meets John, he lists of a load of facts about him, and John is astounded. But we see no actual evidence to support Sherlock's claims, aside from a brief flashback of John's time in the army. And even that is a dream sequence in which you don't actually see John himself. Is he just preparing for his next role?

We never actually meet John's supposed lesbian sister that he mentions at their first meeting, and when John does doctor-y things, he doesn't look very convincing (like checking Sherlock's pulse in his wrist rather than his neck, and falling asleep while working at a clinic).

Hartswood Films BBC

When John first meets Mycroft at an abandoned warehouse, he offers Sherlock's new friend money to spy on him, which John turns down. Why wouldn't John recognise his new employer? Mycroft could have done it anonymously. And maybe he just wants to see how John can handle such a threatening situation.

All this would explain all the odd moments that Sherlock manages to triumph in, in particular that odd scene where he manages to easily rescue Irene Adler from a group of terrorists. But what about Moriarty? Simple, he actually was an actor called Richard Brook after all.

How did Moriarty get all the money to carry out his dastardly schemes? Mycroft, of course. Sherlock's big bro needed to come up with a supervillain with seriously dangerous crimes to go along with him. This also explains how Moriarty knows so much about Sherlock.

In 'The Reichenbach Fall', Moriarty suddenly claims to be an actor named Richard, and was hired to make detective seem like he was solving crimes. While we all assume this to be a horrible and clever lie, what if it was the truth? He actually wanted to get rid of this weird acting gig. And the next time he's on screen, he's gone mad, is forced to carry on the charade, and shoots himself.

VERDICT: OK, it's wrong, but damn, full marks for whoever thought it up.

2. Moriarty has a twin

BBC

"I'm sooo changeable" – could that have more meaning to it?

Could Jim actually have been two people this whole time? Not only would that explain how he has apparently come back from the dead, but also how the hell he was able to carry out all his crimes on his own.

This fan theory has pondered whether we've seen two different versions of Moriarty. One was fascinated with Sherlock and wanted to keep him around (the one we meet at the pool), and the other hated him and wanted him dead (the one who came back in and changed his mind).

Going back to "Richard Brook", maybe he was actually "real", in that he was just one of the twin's real identities. Alongside his naughty escapades, he actually was an actor who was on a popular medical drama. Kitty couldn't have been that shite of a reporter to make sure his backstory checked out. He probably had an IMDB page and everything.

BBC

Plus, there's no chance that one guy could have had the time to date Molly, get a job in IT for a while, have a decent acting career, get interrogated by Mycroft, go on trial, stay with Kitty AND run the biggest criminal web around.

Perhaps the "dark" non-Richard version actually killed himself after going proper mad. "Richard" is the calmer of the two as he's actually been out in the real world for longer, and is thus still out there and waiting to make his comeback. He doesn't want to see Sherlock on on a suicide mission, and wants some more fun with him.

VERDICT: Ehhh… No. Not buying it. NEXT!

3. Sherlock and John are secretly dating and will end up together

BBC

No, this isn't just a tumblr blog, there's some real logic behind it (sort of).

Followers of the 'JohnLock' conspiracy reckon that creators Steven Moffat and Mark Gatiss will eventually turn Sherlock and John's bromance into a full blown romance by the end of the series.

And it's not silly 50 Shades-style fan fiction, but there's been a massively in-depth analysis of scenes and scripts that apparently alludes to a secret relationship.

According to the theory, some fans reckon that the duo's story features plenty of narrative and filming techniques that frame them as a proper couple, not just good friends.

One example is a reference to the ending of Casablanca in 'His Last Vow', and how there are secret hearts littered in their scenes:

BBC

Plus, John doesn't correct Irene Adler when she mentions how the two of them are attracted to Sherlock, even though they're usually interested in the opposite sex.

VERDICT: Wishful thinking. And possibly cheeky playfulness on the part of Moffatt and Gatiss, playing up to the fan shippers.

4. Sherlock helped Moriarty fake his own death

Sherlock is one f**ked-up individual when he wants to be. Could he actually be in on Moriarty's fake death all along? Presuming he's even alive.

The fact that Moriarty is actually alive and well is a theory in itself, but it's the added idea that Sherlock knows all about it that makes it even more juicy.

Maybe the pair of rivals had their own agreement about faking their own deaths, as one elaborate test to see who could pull it off better and more convincingly.

If that were the case, Sherlock's genuine shock and horror upon seeing Jim blow his brains out makes sense, because it looked pretty damn convincing. And now he's all like "Shit, now I have to do it even better by jumping off this roof".

VERDICT: Nope. Why wait an entire series before bringing Moriarty back?

5. Mary is in league with Moriarty

BBC

We hope this one doesn't turn out to be true, because we love Mary and John's relationship. But you never know...

We already know how Mary had quite the dodgy and murderous past. Is that really the end of her backstory, though?

What if she is secretly Sherlock's equivalent of Colonel Moran, Moriarty's second-in-command in the story 'The Empty House' (the story that Mary's debut 'The Empty Hearse' is based on). Mary's maiden name – Morstan – is rather similar to Moran, too.

While some believe that Mary is simply running away from her past, others reckon that she is actually still employed by Jim, and that she was planted to be with John to help destroy Sherlock when he least suspected it.

Of all places, this idea was sparked after a fan spotted something in the official Sherlock colouring book. Mary's wedding ring can be spotted in an illustration of the pool scene from 'The Great Game', eg – the place Sherlock first met Moriarty. Coincidence?

VERDICT: The ring being in a colouring book is neither here nor there. Even Moffat and Gatiss aren't that micro-managey (or devious). But we wouldn't put it past them retroactively turning Mary to be a double agent and pretending she had been all along.

6. Sherlock used to be an MI6 agent

We know little about Sherlock and Mycroft's spiky relationship, but there's one theory that could help explain it a little better. Sherlock once worked for him as a secret agent.

It's easy to guess that Mycroft is the head of the British secret service, so perhaps he once hired his baby brother as one of his top agents.

There have been clues pointing towards a third Holmes brother, so maybe he was also an agent but had a rather nasty death on the job.

This terrible event could have sent Sherlock a bit doolally, forcing him to quit the gig and eventually become a private detective, causing a bit of a rift between the two remaining siblings.

This would explain just how Sherlock also has quite the skills when it comes to kicking ass and infiltrating a terrorist gang and all that.

VERDICT: Well maybe – but why not mention it till now?

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io