Benedict Cumberbatch and Martin Freeman outside 221b Baker Street. BBC

The dust has settled on another series of BBC One's incredibly popular Sherlock, and guess what? We have another cliffhanger to mull over for two years, or however long it takes for the Beeb to rally their sleuthing troops for series four.

We've already reviewed His Last Vow and discussed the cliffhanger, with all the questions it raises, so now let's take a look at the future of the show and what could be in store over the announced fourth and fifth series.

Warning, there are some major spoilers from the final episode of series three below...


The Woman

Five series of Sherlock means 15 episodes, and it's unlikely only one of those will hold a significantly role for the series' most famous female character.

Irene Adler's introduction came in series two's opening episode 'A Scandal In Belgravia', and shocked fans to say the least.

Writer Steven Moffat turned Adler (played by Lara Pulver) into a dominatrix who uses her sexuality to collect compromising images of the rich, famous and powerful. Her introduction was noticeably memorable because she appeared completely naked, much to the ire of the Daily Mail.

As has become commonplace in the show, Sherlock helps fake the death of Adler – posing as her executioner in Pakistan. She's alive then, and after a brief appearance in series three episode 'The Sign of Three', both on Sherlock's mind and certain to return.

Moriarty Sherlock
Andrew Scott as Moriarty, "Did you miss me?" BBC

A different kind of villain

Of course we know that Moriarty will be back, and he'll play a big role in the next series, but there's still room for some variety.

Arthur Conan Doyle's most famous Sherlock Holmes stories have been adapted, and his greatest enemies largely covered. However there is something that could be done to shake things up, something that has more than a little to do with Batman.

In Christopher Nolan's The Dark Knight Rises, Batman was pitted against a more powerful foe. Still highly intelligent, Tom Hardy's Bane provided a different kind of villain for the series.

The first film concerned a group of ideological nutters, and the second was about lone psychopaths causing mayhem. His third and final film however pitted the hero against a character capable of beating him to within an inch of his life.

Sherlock's stories, much like those of Batman, concern the psychological and the intelligent. It's not often a battle of brawn overtakes a battle of brains for the great detective. This goes double for this version of Sherlock, who isn't the fighter depicted in other adaptations or Doyle's books themselves.

Pitting Benedict Cumberbatch's Sherlock against an adversary not afraid to cast the mind games to one side in favour of violence would be an interesting prospect for the character and the series.

Amanda Abbington as Mary with on-screen hubby and off-screen partner Martin Freeman. BBC

Mary Watson's backstory

This was a bit of a shocker wasn't it? What started out as a twist seemingly constructed for impact rather than making any sense, turned out to just about fit with the relatively grounded world in which Sherlock is set.

Mary, who married Martin Freeman's John Watson in 'The Sign of Three', was revealed to not actually be Mary at all. All we know is her initials (A.G.R.A.), that she killed for the CIA and that John doesn't particularly care - saying in the perhaps the series' most romantic moment: "The problems of your past are your business. The problems of your future are my privilege."

Such a reveal won't be left to lie though, we'll inevitably find out more about Mary and what she's done. Episode three villain Charles Augustus Magnussen held information that would damage Mary, so in all likelihood there are figures out there with a vendetta against the former spy.

The third Holmes sibling

Most likely a brother, this would be something new in the Holmes canon and will undoubtedly be a major plot point of series four. The dialogue from 'His Last Vow', the third episode in series three was as follows...

MI6 person: "If this is some expression of familial sentiment..."

Mycroft: "Don't be absurd. I am not given to outbursts of brotherly compassion... you know what happened to the other one."

Sherlock creators Steven Moffat and Mark Gatiss have always toyed with the character's mythology. BBC

Sherlock and Molly

An avenue that clearly needs to be explored further is the potential romance between Sherlock and Molly Hooper, who has always had a crush on the man and who unbeknownst to him got engaged to someone closely resembling the master detective.

The engagement – as we learn in 'His Last Vow' – is off; re-opening the possibility of 'Sherlolly'. In the same episode we also learned that Sherlock is capable of at the very least faking a relationship.

That's progress right? It's clear he liked Janine (played by Yasmine Akram) on some level, even if he was ultimately using her for his own gain. Hmm, maybe there's still work to be done then.

Mrs Hudson's deceased husband's drug cartel

Getting two mentions this series was the drug cartel of Mrs Hudson's late husband. Most probably a throwaway gag adding to the craziness of her character, there's still the possbility that those ties could become the core of a story ultimately showing just how much Holmes and Watson like Mrs Hudson deep down.

Well, it might work...